Being harrassed by exhusbands new wife

I have been divorced going on 4 years now and my ex and I got along just fine (as well as can be expected for the sake of our daughter) until he met the young woman he is married to now. Ever since she came into the picture, my ex hardly talks to me and he has changed so much and not for the better. I don’t have a problem at all with him remarrying, I actually was relieved he got married because he was driving me insane wanting to get back together with me. He went through a period where he would want to see our daughter and then he would not want to see her. She has lived with me full time since she was 2 and he saw her once a week and every other weekend. We hardly ever had problems and we were always able to communicate if we did have a problem. Now, his wife speaks for him and sends me horrible emails, comes to my job and gives me 5 page typed notes that are very offensive, very judgmental, and just down right cruel. I don’t know what to do anymore. My ex and I and our daughter are in counseling and I thought everything was getting better until 2 days ago when she brought a gift to my work that I am my daughter had picked out for a friends bday party. She was furious that I bought the gift because they were taking my daughter to the party. My daughter and I dropped the gift off at her father’s before school Friday morning because my daughter didn’t want her friend to see his gift at school. She picked it out, and even picked out the card and took 10 minutes to write in it, and when my boss saw the package on my car he brought it in and I saw where she actually had opened the card and tore it in peices! I was furious, but I simply took the gift to her friends house and explained to his mother why it looked the way it did, but that I wasn’t going to let the step mom take away my daughters joy and not see the gift she picked out at the party she was going to just because her stepmom was mad at me for buying it. I only bought it because he works full time, just as I do and I didn’t know when he would or if he would even check his email about the party, so I was trying to be kind and save him some time, but that is not the way the stepmom took it. Now, why would my ex have accepted the gift and been so kind to me if this was going to be the result? Does this seem like a jealousy issue or is there something bigger that I am not seeing? This is not the first horrible letter or email I have received. This kind of stuff happens all the time and has been happening for well over a year now. I am sick and tired of it and want to know what I can do to help her understand, she just sometimes needs to keep her mouth closed!!!