Well, it depends on how bad it is and how much she is spending. Are bills piling up because she is shopping too much?

Usually any kind of addiction isn't just about a thrill, but compensation for some void. As with drugs and alcohol, people do stuff like this to avoid the pain they are in and use just about anything as a means of escape as opposed to facing what is really bothering them.
For some it is a rush because they feel better when they get something no matter what, and the thing about addiction that it doesn't really make sense; but it makes them feel better temporarily. It's like the drug addict that knows bills are due, but buys drugs instead of dealing with something like paying the bills.
It's not logical, but neither is addiction.

This person is compensating for something that they feel they need or want. And that person does need help. Especially if the basics aren't been taken care of, like bills.
The best thing to do is to discuss this with that person without judgment, because judgment because you don't understand will only make her withdraw and/or defensive. So take the time to say that you are not judging them, but that you care and are concerned about their well-being. Tell her you don't want her to lose everything because she's overspending, and tell her you are there to help - not hurt.
Good luck.