J.C.
Two things came to mind when I read your post. First, she might be having growing pains in her sleep that is causing her to wake up and be fussy. Try giving her a bananna for desert in the evenings before bed. I had terrible growing pains as a kid and my grandma told my mom to give me bananna's and it worked. Something to do with the potassium in banannas. Second, you said you are pregnant. She may be picking up on this and has some anxiety about a new baby joining the family. You said she will go back to sleep after you or hubby goes in and talk to her so she may have fears about not getting enough attention. At 2 kids are attention hounds, they can't get enough. Since she is so little and doesn't have the words or cognitive ablity to express this she is fussing at night to get attention (any attention is worth it). Try in the day spending some individual time with her and tell her how much you love her. Then spend somemore time talking about her being a big sister and how special that is. That being a big sister is going to make her even more special and you will love her just as much if not more. She may not understand fully what you are saying but she will understand the love part. Good luck!