M.C.
It sounds like she's doing it for attention. If the timing of her going to preschool and the baby arriving are close, she may see the baby as trying to take your attention away from her. She used to be home with you, now baby is home and she's at school. This is very common.
Try to spend some one on one time with her. Do something special that only big kids are allowed to do. Make preschool fun. When you pick her up, have a special treat waiting. Do something fun and spontaneous.
As much fun as the baby's milestones are, try making less of a statement about them. Get a book and write them down. Then instead of telling hubby and family all about it, tell them that baby had a busy day and hand them the book to read.
Good luck
M.