At this stage, I'd be more bothered about her not doing anything around the house and not saving than whether or not she pays keep.
She's obviously a grafter but she's not learning what it actually takes to really keep yourself going, or the value of money and time- just doing her own washing and ironing might be a start for instance. It's amazing what no clean clothes does to a teenager.
If, on your figures, she's getting through seventy five quid a week on clothes and new nails, with grandparents waiting to pay for the driving lessons and the car, possibly a stint volunteering at the local foodbank might be an eyeopener for her about the value of disposable income?