Future MIL Problems (advice needed!)

Not quite sure if this is the best group for this, but I need advice.

I don’t want to seem like a mean person, because I’m truly not, but I really dont like my future mother in law. It’s not just for petty reasons, or because I don’t like her being another woman in his life, I genuinely don’t trust her and don’t know how to handle it.

A little backstory: my fiancé was put up for adoption after his birth mother was deemed unfit to care for him. She was given the chance to get him and his sisters again, but she didn’t come to pick them up. She then got into drugs and a bad crowd, but is now clean for several years. He found her just a couple months ago. Actually, I was the one who technically found her through Facebook. I’ve known my fiancé for five+ years and know he’s wanted this for awhile, so I was very happy for him.

We went to meet her and the rest of his family in August, and all was well until he started getting way too clingy with her (physically) and he put me way on the back burner (more like off the stove completely). I felt very left out because on top of this they (his fam) would all sit outside smoking while I sat inside because I am very sensitive to cigarette smoke and I couldn’t breathe with five people smoking at once. I wasn’t sure what to do because I didn’t want to be impolite and tell them not to smoke at their own house. I ended up telling my fiancé about it and he mentioned it to his family. They lessened the smoking around me, but I remember even after that his mother sat directly beside me and smoked, so the one time he had to actually trade me places so that I could breathe. My fiancé and I talked about it and he apologized for his part because he didn’t realize how I was feeling, but I was kind of hurt by her inconsiderate behavior.

Another issue is that I have anxiety and she is CONSTANTLY over dramatizing everything. She will fly into a fit over the tiniest thing, then stomp away and leave my fiancé to chase after her and comfort her. She is also a liar and lied in front of me multiple times to her other family members. She looked right at me while she did it. She plays like she cares so much but she forgot his name TWICE, even after she was corrected. She is constantly trying to create drama and trash talk the whole rest of the family to my fiancé, then says to those same family members that she would never dream of speaking badly about them.

I’m so afraid that she’s going to hurt him or leave him again, and I am very bad at hiding my emotions, hence the reason my fiancé knows I don’t like her (I get quiet when he brings her up). We’re going to visit again in December (we live 12 hours away) and I’m stressing about it. I’m going to support him but I don’t want to go. As I said, it’s not just that she’s the mother, because previously I had thought of a different woman as his “mother” and I absolutely adore her. His bio mom and I just clash. Does anyone have any advice for me or has anyone also struggled with not liking their SO’s parent?