Bridesmaid/sister In Law Drama

Hello Brides,

My fiance has one sister so obviously I asked her to be a bridesmaid. She has not read or responded to any emails with me or my other bridesmaids during this whole year of planning even though I consistently reminded her they were there. So I had a bridal shower and told my Mom not to invite her, because it was only going to be our family and was 5 hrs away. I wasn't going to ask her to drive 10 hrs. for a small party. However, we chose a date for my bachelorette party back in January and prior to the shower she decided she's not coming to my bachelorette weekend. Then, without my knowledge my mother (who's never been married) asked her for $250 towards the shower she wasn't invited to. This upset her and I think it was tacky of my Mom. I do however think it's rude of her not to come to her only sister in laws bachelorette party. Also, not paying attention to important wedding details when your in someone's wedding is rude as well. Advise on how to handle this situation? And are my feelings valid?