How much to charge? For custom sewing?

This is for my mom, I can't sew a lick, but she wants to know what a fair price to charge for sewing dancing costumes? She has been told anywhere from $5 to $15 per hour. She wants to be fair but also be compensated fairly for her work. They are Ukrainian dancing costumes for kids about size 6x, and they have been pretty particular about how they are made and embellished, with machine stitched and sewn on trim. and each outfit consists of a little dress, a vest, and an apron. So any feedback would be great, and very much appreciated.