I don't think it's a cause to worry or an indication of anything else going on. A 4.5 year old may not have a clear concept of what is means to have a baby in the house, but a child that age can already tell that Mom and Dad are preoccupied, and has probably seen enough babies to know that she is not going to be getting as much attention in the future. Also, having to be the "big kid" or the "big sister" can be intimidating if you don't know exactly what that entails.
My dd was 22 months when baby sister was born. She knew from about 18 months that "baby" was in Mom's tummy and liked to play "baby" and talk a lot about the baby. Since she wasn't potty trained yet, and had never used a paci or given one up, there really wasn't much in the way of regressing for her to do! It was more her pretending, and having sleep problems.
Part of what we dealt with was that as my pregnancy progressed I just could not do as much for her as I used to. At one point my back went out so badly I spent the rest of the day lying on the floor/crawling around. So I taught her how to climb in and out of her stroller, high chair, etc because I could not pick her up.
My feeling is, if the regression is not harmful or disruptive to you, roll with it and just be patient. If it is a problem (like potty accidents), just be calm and consistent in reinforcing the training again. Since she is processing uncertainty and feelings, you need to set a zero-drama atmosphere for her to do that safely.
For the feeding, I personally would just tell her she is a big girl and she can feed herself. And that's it. If she refused to eat on her own, I would just go on with my meal and then say "oh, you must not be hungry" and put the food away. That's not the only way to handle the situation, but it's how we roll in our house.
You really can't stop her from regressing and she does need to process her feelings - just help her work through the stages again and don't make her feel like she's doing something bad or wrong.
I know staying calm when little ones are being exasperating is no joke. Especially with preggo hormones. Good luck, I'm sure everything will turn out fine!