At that age, its normal for them to experiment with taking things that don't belong to them (stealing). I wouldn't be too concerned, but let her know that its not okay to steal, and that you need to be able to trust her.
But I suspect that from her perspective, if you take money away from her, she feels justified in taking it away from you. It doesn't matter that you did it for a good reason; from her perspective, you did not respect her belongings, why should she respect yours, or anyone else's. Before they can really learn to respect other people and other people's things, they need to see that they are respected, and that their things are respected.
She will also learn not to threaten to take money out of your purse if the consequence is severe and painful enough... such as a big bad spanking. But then she is learning to obey out of fear. The trouble with obeying out of fear is that the anger and resentment increase, and go underground. She's likely to simply get sneakier and more hostile. Then you'll have to come up with an even bigger and more painful punishment.
I'm not a big fan of the behavioral technique called response cost. Response cost is when a child loses something for "bad" behavior that they previously earned for "good" behavior. The problem with this is that they never get to feel comfortable, or proud, of themselves for what they have earned - because it can be taken away. It makes the whole positive program shaky.
I don't know what she did that prompted you to take $2 away from her, but maybe you could look at that more carefully and see if you can find a way that is more empowering to her to make whatever amends she needed to make. If, for example, she broke something that cost $2 and that is why the money was taken from her, maybe instead you could approach it by explaining, "you did this; let's figure out how you can make it right." See if she can come up with some solutions on her own. If not, you might make some suggestions: "Well, it costs about $2 to replace this; would you like to pay for it from your allowance?" or "would you like to do some extra chores to make amends?" or "would you like to try to fix it?" Its important that she feel that how she makes amends is her choice, but also that she is not allowed to escape from making amends.
If the $2 was taken away from her for some other kind of behavior, such as being rude or talking meanly or hitting, then that is an odd consequence that doesn't really match the problem behavior. The consequence should match the behavior, if you are wanting to use negative consequences at all (for example, a logical consequence of being mean to other people is that you can't be around other people for a while). But its possible to address behavior without ever using punishments, though that sounds like it might be a big leap for your family, and your husband.
I think threatening to take money from you is a reaction to you taking money from her. I think that particular behavior will stop when she feels certain that her money will not be taken from her.
Do you think you can get her father to agree to not hit her? Hitting just makes things worse. In addition I'd be really surprised if you didn't start seeing some physical aggression from her towards younger children or pets, which commonly happens when children are physically punished. That anger and fear has to come out somewhere, and it's usually towards people perceived as being more vulnerable.
I understand you are horrified by her threat to "steal" money. Did she use the word "steal" by the way? Or did she threaten just to take it back? I ask because "taking back" something implies that she is trying to get what she thinks belong to her. The word stealing implies she is/was planning to take something knowing that it is yours. Intent matters; her perspective of the situation matters.
Also, she threatened and she got punished severely for it. You know what she will do next time? Not threaten but go ahead with whatever she was planning anyway and then make sure she doesn't get caught. She is just going to hide it. You don't want that if you want to remain knowledgeable about the day to day life of your child. If you want to really know her through her teen years, then you gotta learn to live with her mistakes and deal with her in a gentle manner.
And big scary spanks for a 9 year old? No. You can use your words. Your husband can use his words. And she can use her words. I know a lot of people who spank their children when they are little (which, for the record, I am against) using the excuse that young kids are too little to fully understand verbal communication or/and control their impulses. Well, the 9 year old is big enough to understand a lot of things. What is the excuse for spanking her when you could use other consequences to deal with infractions?
Remember, she will grow up. One day, as an adult, she will look back at her childhood and her relationship with you. You may not have to answer to her right now but someday you will.
Did her bad behavior have anything to do with money?
I'm a big believer in natural consequences. Unless the money had something to do with what she was doing wrong, it's just arbitrary and doesn't make sense. There's also a line with punishments that just serves to make the child angry at you and not angry at themselves for their poor choice. (I'm expressing this poorly.) My dh had a habit of punishing ds in a way that he forgot all about the WHY he was in trouble and just knew that daddy made him mad and it was dad's fault he was in trouble.
Threatening to tell other people is odd to me. It shouldn't matter more what other people think of my child's behavior, it should matter what I think. Making her look bad to other people won't always be effective, after all, my girlfriend's son calls her stupid and a retard and she doesn't have a really big problem with that. That's not ok with me, so I really don't care if she thinks it's ok.
Spanking a 9 year old is inappropriate. I'm not a supporter of spanking, I've done it before with my dd when she was younger (it actually works with her). But at 9 there is enough logic and ways to make her understand how she should behave.
I agree with much of what has been said, but also I want to warn that when you spank a child, especially an older child, they stop feeling sorry for what they did, and instead shift their feelings until they feel they are the victim, and they no longer feel sorry for what they did wrong. If she was sorry for threatening to take $2 before, she almost certainly isn't since she got spanked. It really isn't a good teaching tool, and you add the problem that you have to continually escalate the level of violence until you are now past just a spanking and up to a big scary spanking. What comes next? Maybe a change of course where you don't have to escalate or be physical would help calm things down and get her feeling more cooperative.
I'm also confused about why she had $2 taken from her. I suspect that's where the problem started. She either didn't feel that was justified, or it was not related enough to what she did for her to get the relationship. I am not a fan of punishment, but a lot of moms here are, and a rule of thumb for punishments is that they will be most effective if they meet the three Rs - if they are respectful, reasonable, and related. $2 doesn't seem like an unreasonable amount of money for a 9-year-old to pay if they've done something wrong, so I'm guessing she didn't feel it was handled in a respectful way, or it wasn't related enough to the wrong-doing for her to connect the two. In the future, if you punish her for something, you'll probably find that she rebels against it less and learns more from it if you keep in mind those three Rs.
And there are options other than punishing that teach children to do better in a way that keeps you and them on the same side, rather than setting you up as opponents in a conflict. There is a good book called How To Talk So Kids Will Listen that is great for this age group and might give you some ideas about how to handle things in a way that keeps you and your husband and your daughter all working together and talking. It is available at many libraries. As she gets into her teenage years, the more you're still talking, the easier that time will be for her.