soursprout has put together an amazing list!
My eldest 2 are about to go into y8 and y10 (how? When did that happen?), and their worries were pretty much all the ones on that list.
DC take the train to school (after walking by themselves to primary), so that was a worry to them. We practiced the journey, and we also had 2 lots of ‘emergency money’ in different locations for if/ when travel card doesn’t work.
Something we had not thought of: on first day the lunch card did not work (lots of other kids too), but DS was quite shy, and Just went the whole day without anything to eat- even though he had money. I called school to ask what he should do next time and they said esp with new y7, Just speak to one of staff and they sort you out somehow - so that was a good tip to pass on to dc2.
They have both had hiccups with trains, and so it was good to have mobiles and talk them through it, and also so they had an idea
of alternative routes/ stations.
I feel for you OP, I have worriers, and it all seems overwhelming to them at first, it’s a massive massive learning curve - and then you blink, and they are fine.
I know WhatsApp is contentious, but both mine have found their class WhatsApp groups invaluable for homework/ missed work when sick, so encourage your DD to ask about a class WhatsApp group if she feels up to it.
(And I have found the parents’ group helpful for lost kit/ partial information in the early years.)