okay.. so we went through this last year on the opposite end of it as you. My dd started out 1st season with 10 girls. At the end of that season 3 left. At the end of the next season, 3 more were leaving. It was a difficult choice, but due to many factors (mostly gym management/owner) we found it was the right choice for us to leave also . I have posted many times about that, so I won't go farther than to say, you can only claim you're rebuilding a team for a year or 2. After that a parents looking at a gym have to wonder why there are no optionals at a gym (in our case, because the parents wise up and leave before they ever get to that level).
When dds teammates left, it was hard, but each girl was able to say goodbye to the rest of the team (in 1 case, have a pizza party) and things went smoothly. Although dd missed them, it was okay, and she moved on. I'll just say things were not handled well for our departure. The HC/gym manager made an *** of herself and basically kicked us out of the gym (because we were going to be going to the other gym in the area). No nice goodbyes for the girls or explainations of why dd was leaving in the middle of a practice (along with 2 others who were also switching gyms). There were a lot of tears from the remaining teammates because they were confused on why 3 team members were leaving abruptly with nothing said about it. Parents of the remaining teammates were upset about it and no explainations for them either. If I could have, I would have let dd say her goodbyes and I would have wished the team parents good luck in the next season and just explained that the switch was the right choice for my dd, without going into detail. HC totally bungled the situation and to the detriment of the remaining girls. It's not like that behavior hurt us, we were leaving anyway. It was the girls left behind who suffered for the HCs bad behavior. Coincidently, two more girls left not more than 3 months after us. So the team lost 7 girls before the start of the next season. I can only imagine how that was handled!
I totally understand how your dd will feel when she finds out that another teammate has left. Unfortunately, it is part of the sport. I hope that the coaches handle the departure much better than they handled it in our case. If handled properly, your dd and the others will do fine and adjust soon. We keep up with as many of her old teammates as possible through phone and always make sure to send a good luck text before they have a meet. So, make sure to tell her that even if they aren't on team together, they can still be friends and be supportive of each other.. even if they are at a gym that competes against them.
**** Friendships don't end just because a gymmie moves. FRIENDS ARE FRIENDS NO MATTER WHAT, YOU JUST MAY NOT SEE EACH OTHER AS MUCH.
Good luck!