As others have said, I would try to get her involved in helping you. My son was 4.5 when my daughter was born - so a year older. But, he was a huge help during the pregnancy and continues to be a huge help. Part of what I got him to help me with was picking up anything that dropped on the floor. It was just such an effort to bend down and pick it up when you are huge. Now, when I am holding her in my arms, I still don't want to bend down. So, it is now his job to pick things up off the floor.
Also, you may want to start providing your daughter with choices. For snacks - let her pick what she can eat. I have lots of snacks for my son to choose from (yogurt, gogurt, fruits) and he can pick. Plus, I keep snack bags and fruit boxes on a low shelf so that he can go and get them himself. At 3.5, I was still opening snack bags for him, but now he uses children's scissors to open them himself.
My son also picks out what he wants to wear and dresses himself (again, he is 5). I can't remember if he was doing this at 3.5 or not. But, there are lots of little areas where you can start to give her choices to help her feel like a big girl.
Honestly, in my opinion, you need to start training her to help herself more becuase you are having the baby. And, be honest with her - tell her you need her help. My son LOVES to help. And trust me, having him help is not always that helpful to me - sometimes it takes longer to wait on him to "help". But his pride is worth it all!
Good luck!