...if I ask her to look after DD one day while I'm at work, just as a one off? My mum is going to take care of her regularly once a week but has a meeting on this one occasion. DD would be at my friend's house, friend has her own DS about the same age (both under one), I wouldn't be paying her and it certainly isn't going to be a regular arrangement. But I don't want to ask her if it's illegal!
And actually, now I look at it written down, is it unreasonable to ask anyway?