What does this mean?

You assume her behaviour is rational. This is misguided. Whilst there might be an obscure rationale behind all this, the fact that your research (presumably) yielded naught save for dead ends, means either that it's too complex to reverse engineer, or you lack crucial considerations in the decision.
I can describe a somewhat similar experience. For myself, friendship & best-friendship have been fluid concepts - any one would not last beyond a few years. Following the initial meeting, both of us would find interest in new concepts; a few would be mutual, some we would discuss and draw one another, some would be of no interest to one party etc. Over time, we'd befriend people with whom current enthusiasm manifested more intensely, and interaction with old friends lessened consequently, to the point of halfhearted tip of the hat or somesuch. The social obligation at times feels more awkward than the possible future utility of the relationship, especially in a one sided drift. There is constant change in the modern environment, many stimulants to the mind are available; the lifelong bonds of old radiate a mythical implausibility under these circumstances.
Then again, I detect a hint of referring to virtual friendship in your question. Whilst it seems less rigid than the RL counterpart, I've seen some folks maintain their lists with a fervour, correlating with current disposition rather than leaving them forever as loose threads.

Either way, I would advise against all of this. You were / are upset, and thinking your way out is unlikely to succeed. You aren't at war with the lass, and don't have to strategise around her defences. Ask her why. If the connection has dissolved, let go.