I think you need to tell her exactly that, "grow up and get your own life".
I think the shopping thing could be fun though. Just a litle payback for the tourture you have been going through......
But that's just my
sence of humor, kicking in.
You don't have to mean or feel guilty, and the reason she may not have any other friends is because this has happened with everyone else. But if you have tried to explain to her how you feel and nothing has changed, then it may be time to just cut youtr losses.