Why is this your concern, first thing.
Second, I paid for my own tuition and books using student loans. It's not the worst thing in the world. I expect very little from my parents.
If the daughters grades are falling, it has nothing to do with her mother spending time on here. It has to do with the daughter not placing the attention she should on school. She can control her own grades, especially if she's a high school student.
Third, the mother is an adult. If she wants to spend her money on Disney trips then she can do it. It's not as though she's gambling her money away playing the gambling machines every night while in a drunken stupor.