Step-daughter/ex wife drama

So here’s my drama. We had planned on having 4 bridesmaids and 4 groomsmen. His son and daughter from his first marriage to be one of each. His daughter (15) still hangs out with his last ex girlfriend (still friends with his ex-wife) and said no to being a bridesmaid. His ex-wife and him have been divorced for 13 years, and she remarried 3 years ago so I assumed she would have no hard feelings.

So his ex-wife asked if I had a preference regarding the dress for the daughter to wear as a guest. I said besides white stay away from light blue as that’s what the bridesmaid as wearing. SHE THEN PROCEEDED TO GET A LIGHT BLUE DRESS. I asked her if she could return it and she said no, When I asked my future MIL get her a new dress (at my expense) his ex wife texts me. She said I was being a bridezilla and I shouldn't be spending money to get her a new dress. She continued to state I messed up because I should be getting my hair and makeup done with the daughter the morning of and I missed a bonding experience. (that's why I asked her to be a bridesmaid) Lastly I should be thanking her for making sure the daughters hair and makeup are done so SHE looks good in pictures. SMH.