Inlcuding fiance's sister-in-law

I wouldn't. It's a big day and I'd feel weird having someone up there with me that I'm not really close to. I also asked my FSIL, but we get along really well and she's FH's sister. You're not obligated to ask anyone you don't want to. Besides, I doubt she's expecting to be asked being as to how you're not very close and have only seen each a handful of times.

Ask your nearest and dearest, which it doesn't sound like this girl is. You don't have to include anyone out of obligation or because they're family.

We're not having any family in our bridal party at all

I would only do girls close to you that you cannot picture that day without them by your side. Don't start adding random people.

I wouldn't tbh. Actual siblings is fine. But in-law, no. Sorry to say but anything can happen.

My FH's sister is in my wedding party but I didn't ask my FBIL's wife to be in my wedding party. I only see her once or twice a year.

I always think it's a nice gesture to ask siblings of your partner if there's no feuding but I'm against asking partners of siblings (married or otherwise) because breakups can be ugly and it can get awkward at your wedding if that were to happen. I'd say only ask her (or any other partners) if you would have asked her regardless of her relationship with his brother.

I don't think you have you. (BTW, you can edit your post to fix spelling errors even after you post it. )

I have both my FSIL standing up. The one I am really close with the other not so much, but it ment alot to my fh.

If you aren't close to her then don't ask her. I was in my FSIL's wedding before FH had proposed but we are super close.

This is how bp's get insanely large.

Invite the people you're really close to, not out of obligation.

You do not have to include her. You only want your nearest and dearest standing next to you on your big day. Do not feel obligated to have her be a bridesmaid just because "everyone" else is in the wedding.

You don't have to if you don't want too. I'm considering asking my FH's fiancé (who will be his wife when we get married) only because I want an equal number, but I'm undecided. We are close, but not best friends close. I think it's a nice gesture, even though I wasn't asked to participate in her wedding. Don't feel like you have to at all though!