Friend offered to cut my hair, should I tip her?

She is a hair stylist and has gone to school and everything. She offered to cut my sons hair and my hair, how much should I tip her?Her words were"If __(my sons name here)__ or you need your hair cut i can bring my scissors over"But i just wouldnt feel right not handing her some money...should i tip herhow much ?around here it is $15-20 for a cut.but she gets paid by the hour where she works which is $7

um no because shes your friend. Take her out to lunch and offer to pay the bill or something.