Sympathies. I have a 17yo dd with coeliac disease as well, fairly newly diagnosed. Join the fb groups such as coeliacs in the U.K. as they have good food ideas.
I would also approach the college and explain the issue and see if your dc can be given permission to use the microwave, they must have one for staff.
Dd is still at school and pretty much lives on chips from the canteen. Dd doesn't eat McDonald's but I've certainly seen people on the fb group say the chips are ok to eat btw. Dd is vegi so not interested.
Pinterest is also good to search for recipes and save them on a board.
Dd likes a quinoa salad I make. 90g of quinoa, lightly drizzle with olive oil and juice of half a lemon. chop up a pepper, some mint leaves, I add pomegranate seeds for dd. I add chicken for me. I think original recipe had red onion in as well but dd was worried about onion breath so I leave it out now. You could add what you wanted I guess. I use the 3 colour quinoa you can get from Aldi or Waitrose as I think its a bit tastier. 90g of quinoa with added stuff makes enough for 2 portions. It'll keep in the fridge for day 2.
I think some of the John West lunch on the go stuff are rice based and gluten free. They don't need heating.
Dd also likes itsu rice noodles which are like a slightly posh pot noodle but you'd need a kettle.
You can batch cook gf brownies or flapjacks with gf oats and freeze and take them out one at a time.
Hummus and carrot sticks, cucumber.? Fruit.