Start sending your Mother the bills from school :) My daughter is 18 and she is a Junior in High School and she has begged me for nails, I have told her over and over until she can afford to keep up the fillings herself, No!
I have not yet forced her to get a job yet because I want her to finish school and find a job in the summer. But her grandmother took her two weeks ago and let her get her nails done. I was not happy about it but knew in a week or two she will ask for money to have them filled in.
Fine, now it's time for her nails to be filled in and it's Prom weekend. I told my daughter to call her grandma, she asked why and I told her because she allowed you to get them and she paid for them. I told you no, now you need to call her yourself. I also called my mother in law just last night to let her know that she was ready to have her nails filled, when is a good time for you? She asked what I was talking about and I reminded her of "why" I told my daughter no, she now see's the problem. "Oh, I see she says, well let me see if grandpa has the money". I don't think this will happen again.
What I told my mother in law is you are not teaching her to take care of herself, I had to work when I was a teenager and so did you. What if something happened to one of us? Who will take care of her then? She needs to learn to take care of the simple things so when big issues come up and they will she will be ready.
At our kids ages, money isn't what we should be just handing them. Advise is and guidance and then if money is an issue teaching them to repay it will only help them later on. Repaying with cutting the grass or cleaning the garage out or clipping grandpas toe nails! That's the best one.
Grandparents do not realize that they are really not helping just getting in the way, it's hard for them I think we just need to remind them it's our turn to raise our kids and them helping the grandchildren is helping you. So asking the parent first before handing over money should be the first rule.
If you have a daughter close to the same age of mine, your parents must have grown up the same time and money was hard to come by and I'm sure she means well and wants to give her what maybe she could not give you when you were young. If she insists maybe she should give the money to you and let you make that decision for your daughter. Remind your mom what it felt like when her Mother or worse, Mother in Law stepped "butted" in. Good luck!
B. C