The reason these things are on your mind is you're sick of this one-sided taker relationship. Your subconscious is bringing up these instances for a reason. If you ignore it, you risk some problems with yourself down the line. I think your subconscious is telling you a change is in order.
Yes, old friendships should probably have some caveats but somehow this is not cutting the mustard as far as your subconscious is concerned.
I would be personally outraged over the computer situation!! Who does this person think she is that people should wait on her like this!? The behavior is outrageous. A lunch of about $60 or more is in order here, not a mere $25!!
I like Longhorn's suggestion of just being less and less available.
I personally would not take on the stress of leveling with her about the behavior because at this age, she is unlikely to change. As a communications person, however, we are trained to be honest in our communications. You probably should level with her in a diplomatic way. At least she will know why you are less and less available (should you take that route) and it may jive with what some other people have done with their relationships with her.
Cher