So here's question 2:
I bought a sample dress off the rack. It was too big, but I wasn't worried about it because my stepfather's sister's family owns a dry cleaner, and his sister M handles all of the alterations and wedding gown preservation. I called her and made an appointment to bring my dress in so she could look at it. I brought my mom with me, and M said she could alter the dress. It needs some pretty significant alterations: cups sewn in, taken in quite a bit, etc. I was so happy that someone I knew would be doing it. I asked her how payment worked, and she told me not to worry about paying her at all. I was shocked. She told me it was her gift to me, then proceeded to tell my mom how much my SF has changed since he married her, and how grateful his whole family is.
My mom has been married to SF for 11 years, but I was 17 when they got married, and not happy about it at the time, so I never really had too much to do with his family. They come to our family functions sometimes, but I never go to any of theirs because I am usually with other family.
Anyway, I decided to invite M and her husband to the wedding, because I figured that if she was giving me such a generous gift, I should at least invite her. Also, she is my favorite of all of SF's many siblings, and has always treated my mom very well, so it's not like I dislike her and am only inviting her to the wedding out of obligation. I am also going to get her something, probably a gift card to a nice restaurant.
I would like to somehow communicate to her that she should not get me an additional wedding gift, but I am unsure how to go about it, or whether doing so at all is rude. Should I just send her an invite, and let her decide whether she wants to get me a gift, or somehow let her know that the alterations are more than enough? I am just blown away by her generosity.