I'm a camgirl.
Although I'm no way infallible and haven't worked on each and every site, I know a fair bit.
If she's been selling actual digital photos-then yes those people 'own' those photos and can do anything they like with them, If she's selling them via a website, they won't . It sounds as if she's doing both though from what you've said.
IF you sell via a camsite such as MFC, they won't have any contact details or email or anything like that, the sites have these details but they won't put them anywhere 'customers' can see. In fact a lot of these sites will ban a girl from working, if they find out she's doing that.
They harbour a certain amount of responsibility so they try their best to protect-It's part of what you pay for as a camgirl (they take a percentage of your earnings).
If she's selling directly, through her own email address and using paypal, she doesn't have this sort of protection.
As I said, if you could find a way to report her paypal account anonymously, this would put a stop to this with minimal invasion-IF after having the 'talk' with her she still goes ahead with it it may be something to think about.
Using her real name isn't a great thing either-obviously it has the potential to expose identity if these people do have her email address or other contact details.
PM me if you have any further questions related to what she's doing.
Good luck xx