Need your advice on how to say goodbye to an Autistic granddaughter.

Maybe your DIL would help by setting up some facetime or video calls starting now, so that your GC gets used to seeing you on screen as well as real life. Have a story book or toy with you that she is familiar with.

For a 7 yr old girl I would give a cuddly US themed toy that she could associate with you, then keep up on FaceTime when you can

My grandchildren are 4581 miles away, always have been. I used to visit about twice a year but have not been able to of late.
I have to content myself with FaceTime two or three times a week but it is hard.
I try to remind myself that I was 5000 miles away from my parents when there was no way of seeing or talking to them other than an occasional extremely expensive phone call and letters. They coped, I’m coping and you will too OP.
We just fix a smile on our faces and pretend everything is absolutely fine.
I feel for you. ?

I had to do this when my daughter took our grandchildren and went to live far away. Our granddaughter is also autistic although she did understand that they were going a long way away from us.

I was a mess, but I was determined not to let my granddaughter know . I pulled myself together and just spoke about how much fun she was going to have in her new home. I gave her a special "Grandma Box" with self-addressed envelopes and writing paper, cards etc so she could send me "hard copy" letters and pictures. When I was time to say goodbye I gave her a firm hug and told her that I loved her and that we would be Facetiming and speaking every week. I also gave her a little instant camera so she could take pictures of her adventures and send them to me. Then I said "goodbye" and walked out to the car.

They have been gone for 2 years now. She still sends me pictures and little letters, Facetimes a few times a week. Some nights she rings and I read to her over the phone. It isn't perfect but it works. You'll work out your own system of contact, and when the world goes back to normal you'll be able to see her sometimes.

Good luck !

You can find the strength by doing what you’ve done her whole life, by being the best gran you can be and putting her needs first.
And then you can have a good old cry.

It’s not going to be the same, but technology now means you will still be able to see her on video chat regularly, and watch her grow and thrive.