Firmly but not hard hold her hand down and in a very stern tone say "no hitting", then set her somewhere away from you, your husband. She is learning to just express her frustrations since she cannot verbalize them probably, but do not allow it. If he see her headed to hitting, grab her hand and put it down by her side and tell her "no hit", "be nice". Set her in time out now if you have to. She may pitch a fit, which is her getting out her frustration too, but that is better then hitting. Before the baby comes, get a nice baby doll and teach her how to hold the baby, love the baby and be gentle with the baby. I would tell my daughter "we have to be nice and gentle with babies". The night before you bring the baby home, have your husband give your daughter a gift from the baby, making it a huge deal she is a big sister now and the baby loves her.
Get her to help with getting diapers and so on and make sure she feels a part of it all, that will help with the jealousy issues.
Good time now to implement time outs or just moving away from her when she starts to act out. Teaching her she will not get your positive attention if she does this.
My daughter when she was about 16 mos used to snuggle and then all of a sudden sometimes she would bite my shoulder! Or grab my hair and pull hard! It hurt! SO I would say "not nice" very sternly and set her down away from me, it took about a week or so but she got it that I was going to accept that from her and it stopped.