Major fmil road bump long

I need advise on how to handle a major issue that just reared up regarding myself, fh, and his mother. The background is this... she lived in Florida and was hit very hard with Hurricane Michael last oct. Me and fh flew out that day, saw the conditions and offered for her to move to Vegas with us. She did and within 2 months she got a job, new car, and an apartment in our complex. The apartment came days after fh and her fought about her gambling which was nearly daily. She moved into her place and we see her less and less... now it’s at a point that we saw her for on hour or so every other week. We would ask if she could watch her grandchild and she would if we gave her money to go to the casino and put our daughter in the childcare there. When we drive home we pass her parking spot and her car was rarely home. Mother’s Day she complained she was in pain and was staying home so me and my daughter walked over to take a gift to find out she wasn’t even there. FSIL has her on gps and told us she was at the casino. She has been planning on going back to fl for a month now stating she can’t make it financially here. Her income is PLENTY to live off of with extra to spare. But she literally gambles every day now. Fh is very frustrated with her and she is constantly asking for money. She pulled her entire 401k at around $43thousand and it is GONE! My daughters birthday just passed and we called her for dinner and found out she was at bingo and when she arrived here she said how she doesn’t have money for a gift and fh credit card declined. Yet the very next day she is at the casino again. Fast forward to yesterday. It was planned that we make dinner at our place and my daughter stayed the night with her the night before. So Monday I cleaned the house and she called telling me her husband said she can go gamble so we have to go to the store quickly. I immediately called fh and he was highly irritated and told me to just get our daughter, tell her to go to bingo and we are doing something else. So I went and I did. And what happened from there has me highly upset and in tears. I walked in, told her I’m just getting dd and we aren’t doing dinner we’re doing something else. Her only remark was... fh was going to make her go to bingo and I responded that she told me her husband said that... she got highly upset and cussed me out under her breath and cursed me and fh and saying how we just make *crap* up, and the moment I’m out the door with my daughter she slammed the door. I immediately called fh to explain what happened and he told me he told her no money for gambling. She proceeded to tell him he is marrying me and not choosing her and I am a *beach* and will never be her family. Today fh told me to call her and patch it up and I did and she hung up as soon as she herd my voice. So I went to her place and she went off on me. Saying she doesn’t like me as a person. That I lied to her face when I said she told me her husband said go gamble. That I’m making her son choose between me and his own mother, and he chose me instead of her his own flesh and blood, and how she is going to fl to be with family because she doesn’t have family here, and how when she asked about dinner I said no. I didn’t say no I said we’re doing something else so she can go to the casino. She also tossed in how I said she kicked me and my daughter out, and I told her I never said that, I told fh I was already out the door and as soon as my daughter exited she slammed her door. I told fh he needs to go own up to his part and calm this mess down. I was only a messenger and did what he asked and he said I need to own up to what I’m in because I can’t always be the victim. He said if he goes to talk to her it will only look like he is defending me. I told him I don’t need him to defend me. As I’m crying I’m explaining it puts me into a bad situation if she now hates me because we’re family. And how will vacations be? How will it feel? How would it work for me and him if he is with the person his family hates? How would he feel if his mother didn’t show to our wedding? Etc etc etc. he said I need to just leave it alone, but she leaves to fl in 48 hours!! I fear if I don’t fix it now she will have no reason to get over a grudge when she is 2k miles away. I love her and I hate that she doesn’t like me right now, because before this we had no problems. I am so hurt and I don’t know what to do.