Have you considered taking her to another doctor, just for a second opinion? Having a rescue inhaler around might not be a bad thing, but I don't know what they prescribe for children. Perhaps if you explain your worries to your (or another) doctor, s/he would be willing to prescribe one, knowing that you have no intention of using it unless your daughter is in real distress.
In a pinch, some caffeine will usually help a little. It wouldn't work fast enough if your daughter was in a full blown attack, but as long as she's still able to breathe, it would likely help to give her some caffeinated tea, a coke, coffee, whatever you might be able to get into her. Caffeine works to dilate the bronchial tubes. My asthma has gotten worse with this pregnancy and my normal medication is class C, so I've used coke in a pinch to stave off an attack.
The other thing to look at is her diet. Dairy products are a huge problem for many asthmatics, myself included. While I don't believe personally that they cause asthma, they do encourage mucus production. Since asthma in many people is a combination of swollen airways AND congestion, if you can eliminate or minimize the congestion, you can sometimes make the asthma less troublesome. It made an enormous difference in my life when I cut out dairy products. If she eats dairy, try eliminating it for a few days and see if she gets better about running around or acts less wheezy after rough play. If she does, it may be worth it to investigate keeping her off it entirely. If it comes to that, you can PM me for some ideas about how to replace favorite dairy-ridden foods in your current menus. I was raised in Wisconsin and was pretty much made of cheese and yogurt, so trust me, I know how tough that transition can be!
Good luck to you and your daughter...I hope that this does not continue to be a worry for you!