Your daughter's primary should have a briefing session handover with her new school. Speak to the SENCO at the secondary before she starts and ask if she can have a tour of the school.
Work out how she is going to get there. If she is going to catch a bus, drive the route so she is familiar with it and discuss with her what she should do if she is worried.
Most schools have a familiarisation day for new year 7s.
My dd is autistic and didn't go to the same school as her primary friends.she did very well in primary school and is doing just as well in her secondary school, even though she was the only child who went from her primary school. She has a nice little group of friends.
A few things came up that we had to navigate like - she gets anxious if seating plans are changed, she doesn't like receiving test results in front of other students, I have to help her make sure she has the correct books in her bag and PE kit the night before. We put together the things she needs for her period which she keeps in a make up bag in her school bag all the time . If you have any concerns you need to discuss you contact the head of year and Senco.
The one thing that did concern me were the issues that can come up with friendship groups and I recall someone advising me to tell my dd that sometimes the friends they hang around with at the beginning if the year may change throughout the year.
This was good advice. My dd has also asked advice through the year on how to deal with certain friends issues as she sometimes struggles to read social situations but we chat about it and she has managed fine.
She knows which teacher to speak to if she has concerns at school.good luck to your dd. My dd loves her secondary school much more than primary!