Am I overthinking this?

I’ve know my fiancé’s cousin since I was in middle school but after that we never talked again. When I got with my fiancé I ended up finding out they were cousins. Lets name her Amanda. 4 years ago, when my fiancé and I were barely engaged and started to plan our wedding. His mother decided to come in between and use his money to get a car knowing we had to leave a deposit that week. I was furious. So it led to some problems between us and his family. I ended up on his sisters twitter finding out she had twitted saying, “his brothers girlfriend was a bitch” blah blah. Which led to me also finding out, his sister best friend liked my fiancé for a long time and she hoped her bff and little sister to become part of the family one day. My fiancé has a little brother. Which ends being not good later on. After that whole fight and making up with his family. A couple months later, my fiancé received a request from that girl.... I got triggered because it was out of the blue. They didn’t even talk. So which it lead to me adding her and asking who gave her his Snapchat. Which she said, Amanda. In my head I knew it wasn’t good. She knew that girl liked him. And she knew me and my fiancé were engaged and planning a wedding. Also, she had written in Facebook that she didn’t like no female contacting her man. Unless they knew her well. Which led me to ask myself, why would she do that? I just thought it was just me overthinking. It took me a while to let it go but eventually I did. Till now. Recently there’s been something going on with Amanda and us. That kind of makes me think... she wants the worst for us..... but this is an example of the first thing she did and now is bothering me again. Do y’all think she was hoping for a bad outcome? or it was a mistake?