My heart aches for you, Sebella, and for your gd, as well. It seems clear that you were close to dd and gd, so the difference between then and now must seem quite drastic! It's also very hard for me to understand how a loving mother can cut her child off from someone that has been such a big part of their life!
If it' s any comfort, it's not unusual, Ime (in my experience) for kids to have difficulty settling back into their usual routines after a fun visit away from home. Perhaps you've noticed that, too, over the years. It's also not unusual, from what I've seen and heard, for parents to blame the people in the house where the child was visiting, especially if they don't have too much experience with having their child visit other people. IOWs, you're not alone.
The fact that gd is close to you and wants to return to your home probably has made them extra-sensitive about this. Also, I take it the rules in your house are different than theirs - fewer and less strict. So perhaps that makes it especially hard for gd to get back into their strict routines. She may have even defended herself by pointing out that you don't demand the same things of her. Idk, but, sadly, they may think that keeping her away from you for now, will help them bond as a family and get her to accept the new rules. Hopefully, if they feel more secure, eventually, dd will reach out to you again.