Does she know about the baby? If she does, then I would say that she is reacting with some anxiety, and this is how she's expressing it.
However -- it could also just be normal 2 yo behavior.
|scream uncontrollably at diaper changes
Resistance to diaper changes is normal at 2 yo. and very very difficult to stay patient with. I've had my very worst most shameful parenting moments while struggling in this exact situation. One tactic that was helpful to me was to keep small objects that I only allowed my son to hold during diaper changes. Little trinkets that he was attracted to, that I made seem "special" and just for this hard time. A medicine dropper was a big favorite. The TV remote was another.
But I also think the behavior indicates that she is on the verge of potty training readiness, so if you haven't already I would start reading her books about using the potty and get her a little potty. She may not start catching on for a long while yet, but she is frustrated and wanting control over her own body, so its a very good time to start explaining this special way that she can be in charge of her body and maybe get rid of diapers eventually.
|I try to be very calm and logical
I can appreciate the effort involved in this tactic, but I'm thinking she has a very emotional sensitive personality, and that this is frustrating to her. Some children who express strong feelings *need* those feelings recognized and validated. Reasoning is a better tool for when they are calm. But in the moment they need to know that Mommy understands how frustrated they feel, and that its okay to feel that way. It can be scary and upsetting and lonely to feel so freaked out. Not all kids are this way -- my children are more "logical" sorts. But I've spent time with and cared for children who are like your DD -- and it helps enormously to focus on validating feelings.
|What are some consequences I can give her at this age for her tantrums and throwing things?
Consequences at this age are not the best approach. And consequences for feeling angry are never helpful because they make kids MORE angry. It is important to learn constructive ways of showing anger, anxiety, frustration -- but she is very little and even if she has some verbal skills, putting words to feelings is a very high level task. Some adults have trouble with it.
For tantrums, I think the best thing is to accept that they will happen and that its okay. Do what you can to prevent them in terms of making sure she naps and eats well. But then when they do, accept that she's flipping out, that kids do this, if she will let you near her than talk about all the strong feelings she must have and how hard it is not to know what to do with them. In general, do not give into what she wants. Its not a great idea to teach her that tantruming gets her what she wants. But you can still be firm and show empathy/affection at the same time, kwim?
For throwing things -- my approach was to keep a basket around with soft objects that are safe to throw in the house. Foamy balls or bean bags. And when my child threw something innappropriate, I would quickly intervene and say, "Oh, we don't throw that -- but you can get your angries out by throwing these instead."
You are not a failure -- all kids throw tantrums. I think the biggest step for a parent is accepting that we are not always 100% in control, and accepting that its okay/not our fault when our kids have strong feelings.