A lot of the Cubs in my Scout unit get theirs from Lidl and Aldi middle aisles, and Decathlon. Regattas is also good or Mountain Warehouse.
What does she need? Tent, sleeping bag, sleeping mat, rucksack, crockery (plate, mug, cutlery) etc? The full kit?
Or more like a sports bag to carry her clothes, a sleeping bag and something to lay that on? You could ask neighbours, especially any into scouting or family camping, if you can borrow things. Unless there’s a long walk from the car/transport to the tent, a normal sports bag should be fine - but a small backpack (like a school bag or pe bag) is handy for going out and about.
Rummage out the winter wear. Fine her warmest PJs, a woolly hat and something thick socks for bedtimes - and she may want to wear a hoodie as well if the nights are chilly. Covering your head makes a HUGE difference to sleeping in tents! At least in Irish/UK weathers.
if you have any kind of bag that will hang on a door handle, that would be useful for bringing wash gear to the toilet block and keeping off wet shower floors. A travelling wash bag with a hook, a small cotton tote bag…
Have a good look around home before going mad buying things. If you have any plastic picnic crockery, that’s perfect.
One thing I’d definitely make sure she has is a torch - preferably both a head torch and one to carry in her hand. And you can find cheap versions of both (some are wind up, but others need batteries so send a spare set of batteries in that case).