SIL turned into a stranger?

I (23F) & sister (28F) have always been super close. We fought growing up, but became best friends once she left for college. We didn’t have a great childhood, and have both done a lot of work fostering a relationship with each other where we could process a lot of that trauma together (and in separate therapy). My sister came out at a lesbian around 2020/2021 and began her first wlw relationship in early 2021.

For the sake of this post we will call my sister-in-law “Shirley”. When Shirley and I first met, I thought she was amazing for my sister. Shirley seemed centering, and more down to earth than my sister who is at times somewhat high strung. I became what I considered close friends with Shirley, even living with her and my sister for a period of time while I was completing college. They recently got married in October of 2024 and had asked me to be both of their honorary roles for the wedding and my now fiancé to be in the wedding party. Everything was seemingly going great.

Fast forward to January of 2025 and my sister says she’s had a mental health episode, and they decided that Shirley needs to be fully in charge of both of their finances because my sister was not in a stable place. They also chose to announce that they had decided to move to Ohio (several states away from our family). Obviously a few reg flags went off for me, but with a new marriage involved I didn’t feel like it was my place to “imply” anything. Shirley already had gone no contact with all of her family, and frequently told people in conversation that they should do it too.

They completed the move in May, without jobs and much more debt, they seem to be happy, but the second they moved Shirley fully stopped communication. She no longer answers in any group chats or dms with my fiancé and I or with any of my family. When we have called or ft my sister she fills us in on everything going on with them / Shirley but Shirley is just in a different part of the room but silent?

My partner and I got engaged in July of this year and as we get further into planning we are both at a loss of how to move forward with this situation. My sister texted the family gc saying they weren’t coming to Thanksgiving or Christmas because Shirley has to work. This is also during a time where my fiance and I are living much closer to my family than we have in the past. My sister has messaged my mom multiple times saying how sad she is they can’t make it to the holidays and basically that she has fomo, but yet they moved several states away seemingly just for fun.

I could get Shirley or my sister acting different if we had beef as a family or we were unsupportive, unkind, or unloving. My reason for the post is to get any takes on the situation or advice on how we should move forward with our wedding / relationship with them? I obviously want my sister as my maid of honor but am struggling to imagine being comfortable with Shirley being there on the actual day of.