My DS is 18 in care work. We went on salary calculator and worked out how much his basic take home pay would be after tax and national insurance.
We talked about how you split your money and I told him of something I read on MSE, I think, which said 50% to bills, 30% on living expenses, 20% to savings. He agreed that made a lot of sense and so splits his money as above, however his bills money he pays half to us and half to an ISA so that he can save for a house deposit. He should be paying us £400 a month however we take £350 and the other £50 gets added to his ISA. In reality he brings home a lot more than basic because of the shifts he pulls. We have advised him to save 1/3 to his ISA, 1/3 to general savings and 1/3 for fun.
We wanted him to learn how to handle his money in a safe environment at home and get used to saving. We also wanted him to learn that he had to pay his own way in life and nothing is for free.
He is getting a very good deal, he would not be able to rent anywhere with all the same comforts as he has at home. He is getting the opportunity to save for a place of his own and help us out with the cost of living rises.
He is also expected to keep his room clean, empty the dishwasher, do his own ironing and any other add hoc stuff we ask him to do. We all work, we all make the mess, as adults we all have to do our bit round the house. He is not a kid any more and has to contribute.
I would sit your daughter down and show her how much everything costs, council tax, food, water, gas, electric, insurance, cleaning stuff, rent/mortgage, internet etc etc. She might then see how good a deal she's getting!