Crazy sister inlaw!! Sorry to post twice just really need an outsiders advice!!

Didn't know where else to post this but I need some advice. I have been with my now husband for 5 years. Ever since I met him his sister has been jealous of me. And I do mean that conceited bc she is beautiful. She has always competed with me and it just drains me. We waited 4 years before we got engaged bc I was 16 at the time and he was 18. Well she met this guy and kept asking when we would get engaged and I told her we could probably afford it that summer. Well she was with this guy for 5 months and Bam they got engaged. I was so upset bc I waited 4 years then his sister jumped ahead of me and did it. I got over it. Well we got married this past December. She really wanted their wedding in the fall and I had always planned that too and she put her date right next to mine. So I moved it to December and loved it. Had a beautiful wedding. Well she decided not to marry that year. And now all of a sudden she decided to marry I'm December. A day before our anniversary. I am so pissed I won't lie. And on top of it she copies every single thing I did. I try to take it as a compliment but I can't. She is the same age as me but doesn't act it. She is even serving the same soups! I need advice on how to not just blow up!! Please help me!!!