I can say from experience, just because the parent is bad doesn't always mean the child is bad. The mom should be concerned, but I'm sure if she could spend the time she'd probably find the friend not so bad.
I don't agree with what makingblah said, if your kid is hanging out with some pothead who has a pessimistic view on life, they probably shouldn't. That most definitely not the case here, but that is an example of a situation where a parent should step in.