Perhaps she is feeling a bit anxious about the bub and any attention is good attention in her eyes so could be part of the reason she is acting up.
I have noticed increased whining and demands for my attention from my 5 and 2yo's. Usually when I try to grab a bit of a rest but more often if I'm on the phone or in the kitchen cooking.

One thing that I can say that could help is to totally change your evening routine. Mason used to go on the rampage and demolish his bedroom every evening. Sometimes before dinner, while I was cooking, other times after but it would happen every night. The way we got around this was to have dinner prepared earlier in the day. After dinner instead of doing the dishes we would do the bath and PJ routine, then go play all together with his toys for a while, then it was story time and bed. During summer we would all go for a family walk to the park then when we got home it was bath, PJ's, story & bed.
During this time the TV and the PC was off and it was all attention on the kids. And yes it helped!

I think you need to adjust your own habits to create better behaviour in your children. Having a child with Aspergers Disorder I know full well the type of havoc destructive habits or routines can cause and if she is doing the same thing every night then you need to get serious. I'm not saying that your DD has the same issues as Mason does but kids can be complex little beings and habits can be hard to break, especially if she thinks the only way she can get your attention is to act in a certain way.

I actually agree with what Kaydee says too. I don't think it's a good idea to threaten to take her to the hospital. She has probably worked out by now that you won't follow through with it which is why she still acts up.
Why don't you try taking away a favourite toy or DVD instead.