Your sister should of not automatically assumed that she would be the maid of honor just because she is your sister that's was immature of her you need to talk to her 

I don't have a sister, but I have two best friends. I couldn't decide between them who to make my MOH so I asked one of them to do the honours of standing next to me during the ceremony and the other one to make the speech at the reception. 

It is your wedding! Not theirs!! When they get married then they can plan it however they want. You do whatever you want to do and how you want to do it. And if they give you a hard time tell them that they don't have to come. Planning a wedding is already going to be extremely stressful and you're going to need all the help and support you can get. Either she gets on board or stays home. 

You can have both,  but it's your wedding. Whatever you want to do. Just take her to a dinner and explain the situation to her. Maybe even before you get married do a special sister weekend getaway. My best friend was my maid of honor over my sister, but that's because my sister and I were not close for the last couple of years. She was making some bad choices and blowing off the family. But just remember it's your wedding. 

Have both! 

Sorry about the situation but I'd tell them its my choice and I expect you to play nice the day of. its YOUR wedding and honestly they should be happy they are even in it either way.

In getting married in feb & I will be having witnesses as it will be in a registry office I have one sister who I'm close with but im closer to my mom so I have asked my mom to be my witness..My sister probably won't be happy but tough its my day..Choose who YOU want its your choice no one else's

I choose my best friend over my sister. My sister was a bit upset but she got over it. I was very close to my friend from the time we were 7. But she then meet a waste of space bloke. Got pregnant within a month and she completely changed. He walked out on her while she was 36 weeks and started seen somebody else. She took him back when the baby was born, then she found messages on his phone where he was bad mouthing her and saying he was only with her for the baby. She ask my advice. So I was truthful and told her she deserved better. That he was not worth it. She took him back again and I think iv heard from her 3 times since November. I had a terrible fall and ended up in hospital. She never even rang to see how I was. Then I had a chemical pregnacy. She wouldn't answer any of my calls or txts. She hasn't been there for me. She choose to fraise me out for a cheating lying scumbag. So I left her a message saying my sister was upset not been my maid of honor and would she mind if I had her instead. She just txted me back saying yeah whatever. I'm sorry I picked her in the beginning. Family is family. They are with you through thick and thin. Friends drift apart and forget about you. That's what happened me anyway. So I now have my 2 sisters and my future sil. Best decision iv ever made.

I have the same issue going on. my sister has never been active in my life or as a sister to me my best friend has gone above and beyond for me every time I've needed her. it shouldn't matter that your sister is mad at you. this is your wedding not hurt if you want your best friend to be your maid of honor you should do it and feel no remorse for it. Especially if your best friend has earned it. and I'm guessing she has because she is still your best friend lol

My sister is psychotic I chose my best friend as my maid of honor and didn't even have my sister as a brides maids and I am so glad I chose that. My BFF could handle my sister and take her on in an argument.