My Monster of a Sister in law in Life Lessons

So here is some backstory.... My future sister in law lives 3 hours away ( where my fiance came from) and she comes to visit on occasion. She is pretty upset that my fiance moved here to live instead of living in his hometown with her. Anyways she came down to visit this weekend (and brought some friends her age to hang out with my younger sister for the weekend, she is two years younger than my fiance, three years younger than me) and this is how it went:
lets start from the beginning, Friday night she drove down here with her friends - me and my fiance went out on a date and she is blowing his phone up (where are you, when will you be here, I want to see you, who are you with, what are you doing) (crazy jealous girlfriend things) as we are on our way home. She tells him she is at my sisters house, then meets us at my fiances house. That night I went to my parents house to sleep and my fiance went home, my fiances sister came into my room to talk to me - we are talking about wedding stuff and how its close and its really getting real, and she continues to tell me that this is a big decision and I probably should rethink it, and how we really don’t get along that well, we just fake it all the time (which is a lie) and how she thinks he needs to move back to be with her. It caught me off guard a bit.
Then on Saturday she wanted to hang out with us - my fiance had other things to do and i went to a garage sale with my mom and best friend - so fiances sister and her friends came with us. Then at dinner fiances sister told my fiance that she moved his laptop off the kitchen table because she takes better care of him than anybody does - while I was standing there. That evening she had made plans to go out with her friends and my sister, me and my fiance made plans to go hang out with some of our married friends - fiances sister was upset we didn’t bring her with us… my sister had made her first cheesecake the day before and they cut into it after they went out - everyone loved it except fiances sister - she rubbed it all over the plate and said it was gross (after my sister made it gluten free for her).
Sunday - I was sick at home but she went to church with my friend and sister - and there is a kid that is autistic and loves to tell everyone “hi” he tried to tell her hi and she ignored him then she came home and told me he was very annoying and it ruined her day and how she didn’t like him talking to her - very rude…
after church my friend came home to check on me and we decided to go out to eat (me, my friend, my fiance and my cousin that my friend likes) while fiances sister hung out with her friends - later to find out she was ticked that we didn’t take her with us. While she was hanging out with my sister and her friends she told them she was upset she didn’t get invited to go with us and she would much rather be with her brother than the girls she was with, and she told my sister that when I have kids she will be the favorite aunt because the kid will live around my family so she would be the favorite…
along with all that she was very disrespectful to me, my best friend, my mom, my sister - all while being a jealous girlfriend to my fiance - she followed him around everywhere, texted him every few minutes, demanding to know who he was with or talking to, why, what he was doing, where he was going - all those things…

I don’t know how to handle this or if it will get worse when we do get married…