Should i have my sil in my bridal party?

I’m getting married officially (we’re already married from a cruise but don’t really act as though we’re married and not many people know so this is our legit wedding) in a year and a half. My fiancé is having my brother in his wedding party (we each have a sister and a brother) because they’re close.

My fiancé has been like a father to my brother, who doesn’t have one, and my brother loves spending time with him. My fiancé is also having his own brother and a few friends.
I’m having my sister and a few friends. Originally, I had resolved to having my SIL as well (fiancés older brother). I grew up thinking this was normal. However, she doesn’t like me at all and barely speaks to me at events.
Over the last 6 years, we’ve had one casual conversation at the beginning of each event (how are you, good to see you etc.) then she avoids me for the rest of the event. She also avoids spending time with either of us if I’ll be there and will only invite my fiancé over to do a task so that I don’t come with him.
This was something that made me really sad for a while because I wanted to be close with my fiancé’s family. Just recently I realized this won’t change. It’s incredibly uncomfortable to be around here (she doesn’t make eye contact, doesn’t make small talk even if I try, and tries to walk away immediately) so I literally cannot imagine having her in my bridal party.
However, I don’t think his family realizes there’s anything wrong. She was in BIL’s wedding a few years ago on his wife’s side. This would be the only wedding she’s not in. She does have young kids so I could include them in the wedding instead, but I still think it’ll be pretty obvious that my brother is in it when she isn’t. What is the correct etiquette here? And if I do have to include her, is there a way to do it without awkwardly asking her with a gift or having my fiancé ask her or something? As much as I don’t like her, I would much rather just have her than do something outwardly rude.