Clothing Allowance for 11 year old

[Sunnylodge]

My 11 year old has just started secondary school with a full uniform. She got a mobile phone for her birthday in May. One reason is the school is a chartered school bus away - so if she needs to stay for clubs and stuff after school we have to sort out a pickup.
At the moment she gets 3 pounds a week pocket money and up to 10 pounds a month on the phone. (So far - she has only had 20 pounds over the last 3 months.)
I want to start a clothing allowance - probably integrated with the pocket money.
Any ideas on amounts? Or websites with good data?

We started a couple of years ago when dds were 11 and 13 giving them £30 per month and still give them that amount.
The money is totally separate to pocket money and is given to them when they go clothes shopping. Any money not spent on clothes during that trip, they give back to us. They also give us the reciepts for the clothes they have bought. A) so we can check the amounts and B) so we know where it is if the clothes have to be returned.

BTW This money is only for tops, jeans and jackets. I but pjs, underwear ans shoes.