So she has problems, are you willing to hold her hand while she learns to be a better, more efficient user? Sounds like that would be no fun with her. So unless she's willing to learn how to control her RAM usage from someone else, or you feel like enduring her attitude just to patch things up your right to just buy back the unit as amicably as possible.
Just a tip- it helps to proactively spot a pissy customer's problem and delicately resolve it without challenging them. Once challenged, their hackles rise and things get divided as they did in your situation. Customers are wary when they don't understand the machine they are using. (I've been an auto mechanic, so I sympathize with your experience.)
It takes a lot of people skill to help a customer like her see how to enjoy her computer more as it is. It would take a commitment, and it sounds like you were just doing a favor and had no intention of re-educating them as a part of the deal. I can't blame you, and I see why some of the above posters don't help friends with computers...It's just too damn bad we do business with strangers rather than friends!
