I don't quite understand your business relationship with her. Does she send you work or allow you to use her as a referal? Is there a reason that she thinks she's "earned" these perks? What would happen to your relationship if you did stop doing these "favors"?.

If the only issue for you is the cost of supplies - make her purchase them for you - ink and paper both. You can even label the ink "her cartridge" and use it just for her requests.

I've learned that passive-agressive is not a good strategy. You need to be direct. Invite her out for coffee (neutral territory), and tell her exactly what the problem is and how you are very concerned that it could damage your friendship. and then mean it.

Ultimately, if she really doesn't get it, then she isn't a real friend.