Very quickly we had a request for a cushioned mattress protector and an extra pillow.
Send her with something to wear for a meal out (mine used to go for pizzas with friends and sometimes their parents who were in the area). Her school also had a few social functions which required evening dress and heals. DD initially had a short black clingy dress and a silky red mid calf one, both really cheap (£20) but did the trick.
School will have toiletries for emergencies, but I sent mine with a good supply of everything. They weren't meant to have paracetamol in their rooms, but she had a few occasions of bad period pain, horrible flu bug, and it was better to have something in her room rather than having to go down a slight of stairs.
I don't think DD every needed a sewing kit. Sent her with a shoe cleaning kit, but I don't think it ever got used.
Don't forget dressing gown and comfy slippers.
Oh, and I sent mine with chocolate. Maybe give her a little extra money to start with, it was a big thing in the first term going to the local M&S/Tesco and buying treats.
I bought some massive laundary bags from Amazon. They're brilliant for squeezing their quilts in, packing heavy files (which she'll want to bring her next year to work on in hols), miscellanous stuff that hasn't been packed when you arrive to pick her up.