Only just seen this - it's hard for you and them, for sure.
Family reunification only applies to young children- but not adult child and grand child. Did the school tell you you could bring adult + GC?
And this is he nature of things- adult daughters can rarely live in peace with mum and vice-versa. I love mine with all my heart- but could not live with either for more than a few months. When DD" returned from abroad- running from a controlling and violent freak- we had a fabulous time for the 4 months she was here- but we both knew it could not last forever. Normal - nature.
Thanks goodness you can be at the airport in a couple of hours than short, cheap flight to UK- and vice-versa for your daughter. She can of course come for 3 months anytime, and look for work here- as UK has signed agreement with CH.
You did mention you might move to China - can you imagine how much harder that would be?
Our grandchildren always used to get upset when we left, or when they left here after a holiday. They still do, but at 11 and 13- they understand the situation. In many ways, because we don't live on doorstep- our time together is really special and so precious- for us- but I know for them too. Granddaugher wrote for her school magazine how our house is her favourite place in the whole wide world - and how 'cool' it is to go haring down mountains on skis with Granny and Grandpa, and kayaking, wild animal watching (Ibex, Chamois and badger watching)- and so on.
Heart goes out to you- we should meet up soon - Montreux perhaps, for a good natter. We will be in the next Valley to you in 2 weeks- so could meet up in Sierre or Sion.