Hi M.,
As a single mother I know how hard it is to raise a child all by yourself so whenever someone offers to help, it's a major blessing for me. However, she is definitely taking advantage of the situation. Being 2-3 hrs late picking up her child is unacceptable, especially when she does it as often as you say she does. I can understand once in a while, things happen but it sounds like it's becoming a habit. You definitely need to talk to her about it and be gentle on how you approach her for the children's sake. If the girls have a strong bond this may jeopardize that friendship, depending of course on how the mom takes it. Communication seems to be the key here. Set a time with her in which she needs to pick up her child as well as a "no later than" time (9:30pm is a bit too late for a school night for any child), and if she is going to be late she needs to call and be HONEST and STRAIGHT FORWARD on what time she'll be by. She'll just need to schedule her clients accordingly or make other arrangements to have her child get picked up on time should she have to stay late. Don't feel bad for doing this, believe me... you'll be doing her and her child a favor. If she continues with this behavior, who is going to want to continiue to give her a helping hand. If she's doing this to you, she probably does it to others and when people take advantage of it.. people stop helping and as a single mom, her and her child will lose the benefit from others helping them. Take it from a single mom :) Whatever the outcome may be, know that stopping this behavior was the right thing to do. BTW... you are AWESOME for giving that child some love & stability while in your home, kudos to you!