I didn't deal with this age separation - My kids are almost 4 years apart. But I don't think she is doing anything I would really characterize as regression. She is barely two - they are really little babies until they turn four. I wouldn't expect too much from her - she is behaving like a two-year old. My kids both "regress" sometimes and has nothing to do with a sibling or even a major life change. They are little adults and sometimes,like us, they need more attention or affection and this sort of thing is how they get it. My oldest did it before I was ever pregnant and still does from time to time. It is simply their way of checking-in to make sure they still have your attention. She would be doing this anyway, it just so happens there is a baby coming.
However, that does not mean that she is not feeling insecure. She probably isn't making any sort of direct conection yet between the baby and her feelings. She can't really comprehend what having another baby means. I mean, in some ways, you don't really comprehend it either :) However, she can sense the anticipationa and excitement. She gets those feelings by osmosis from you. She isn't capable of interpreting them, and it freaks her out, so she may be looking to know she still has your attention and looking for security. She is sort of saying, "Mommy, are you taking care of me?"
After the baby, I would make sure you make some daily focused time for her. Preferably, keep up some part of your routine with her. For instance, if you always put her to bed, or you always make her breakfast, try to do that and especially just you two, without the baby. Even if it is just that you do the bedtime routine everynight, that 30 minutes alone with her (no baby) will mean so much to her. My daughter is five now, and she is very good at saying, "Mom, I want alone cuddles with you." Your daughter can't say that, but she will still feel it. I really tend to feel bad for them, because it must be so frustrating not being able ot express what you need.
Another piece of advice: When she comes to meet the baby at the hospital. make sure you are NOT holding the baby. Let her come in and see you (HER Mommy) waiting for her and give her a big cuddle. Then, bring the baby over. Let her feel that she is still number one with you and that this interloper is not taking her spot.
I felt (and still feel) a lot of physical demands since my second child was born. You hold a newborn so much, and especially if you are nursing, it is so draining, no matter how good the baby is. It is hard then to have an older ohild climb all over you at the same time. As much as you kind of have to tough it out, make sure you have some plans to free yourself of the kids for a little while each day, so that when you are covered in kids, you can enjoy it.
Congrats, enjoy them!