debate

So my daughter lives with my mam due to health at the time, well I just found out that my sister is getting married and she's already decided my daughter is her brides maid without even asking me if I'm OK with it, I'm getting married November and I have a feeling my mam won't allow my daughter to travel down here for mine, my brother has stated he will travel down with her though. I've been crying all day as I never get a say in my daughters life and I'm getting pushed away, I feel as if my sister is trying to replace me as a mum, I have a 2 year old and I'm currently pregnant I'm going back in for custody of her as I think it's best I was happy her been there but it's getting out of hand, does it seem fair my sister demanding she's bridesmaid without my permission I am her mum? I do have parental responsibility for her.