OMG! I had a much littler "big sister" at 22 mos when the baby came, but she did a lot of the same stuff. I think...kids get scared they are being replaced. I also was her sole entertainment. So I mixed up the activities to give us both a break.
I did several things to ease her acting out. A good talking to helped remind her, I was always positive & reaffirming that she is my #1 only first child, that sort of thing. Then I started giving her little jobs that made her feel like a big girl. The tone was, "big girls get to ...." fill in the blank. (help mommy bake, take real pictures with a (cheap) camera or some special outing.) She picked right up on that & added that "babies can't do that."
She became very possessive of me, a big turn around. And she was a great big sister.
I could go on all day about the young mommy years as these times are special & wonderful & trying. Like life. Make sure to have some "alone with daddy time" too. She should be learning to share you. I wish you So Much good luck!