T.F.
I would never allow my 17 yr old to post on a website to babysit for someone we don't know. There has to be a better way.
Our HOA has a secure website where you can post for babysitting, house/pet sitting, tutors, etc. My daughter is on that one because it is affiliated with our neighborhood. STILL.... she is very picky and only babysits for people we know or have friends who know them.
Does your neighborhood have a community pool? Go to the pool in the mornings and be around when moms are there with their children.. Get to know neighbors, use word of mouth to your friends, church, school, etc.. My daughter is a cheerleader and is active with her school and has met families through cheer camps when she is working with the younger children. Network.
Help her network... Along with running our company from home, I also substitute teach at the elementary school that our neighborhood feeds into and my daughter attended K-5. My contacts at the school, with parents and children have helped my daughter get regular sitting jobs. We have neighborhood social activities and she ALWAYS goes because it is a chance to meet parents, children and network.
She currently has about 4 families all in our immediate area that she sits for regularly.
You just have to get out there and spread the word. Let your friends and neighbors know she is available as well.. they can help network.
Good luck