Now I know she is 18 - yes she needs to sort it out herself.
The trouble is what the law says and what happens can be different (not saying it's right). I suppose if she is paid for all the hours worked it is not as bad but to be honest I would rather have less money and be able to eat.
My DS used to work earlier and later hours than he was supposed to as he was under 18. He was paid almost double the NMW so I figured he was being paid as an adult he could do the hours. If he had been on NMW I would have told him to say something