Sister said horrible lies abt me

I have an identical twin sister and she has always been more bossy than me and I've been the more reserved one of the two. Long story but I found out she had been telling ppl horrible things abt me such as that I had an std, couldn't have kids, I was a slut etc etc etc(all TOTAL lies). And those are only the things that have gotten back to me over the years. I am now engaged and pregnant and she was so angry and jealous she even told ppl that my fiancé said he loved her and he said she was more beautiful than me etc etc hahaha. I confronted her in front of my fiancé and she said omg you're such a horrible liar, acted like she never said such an awful thing!! (Of course my fiancé thinks she's crazy and awful) Hahah it's insane and fking hurtful and worst part is I had no idea for yearsss and thought she was my best friend. I always worry abt her and care abt her so much. Now seems to be a bit better between us but I never know because how can I ever trust her?? But I dunno how to deal with that I don't understand how she could have been so awful, I've never done any such thing to her. I am really hurt and I dunno how to get through it. I'm due next month and I don't want negativity in my life or anything bad for my baby. Anyone had such a situation? Any advice on how to deal?