I would like some advice please, but first, some back story.

I went out with this girl for about a month last year, having both liked each other for a while beforehand. Things didn't really work out, and I broke up with her, fairly amicably. (It's a bit more complicated than that, but I'm not sure how relevant that is to my question, plus the full story reflects pretty badly on me)

Anyway, we stayed friends, and things were fine for a while, until one night I got a bit drunk and said some really quite shitty things to her. Understandably, she was quite upset. The next day I realised what a dick I'd been, apologised profusely, and agreed to give her some space. I left it for a couple of weeks, then texted her to ask if she wanted to be friends again.
Her reply: "Not really".

This was about three months ago and we basically haven't been on speaking terms since. She will tolerate my presence with mutual friends, although no eye contact/conversation is made between us.

Aaaaaaand, that's that. Today though, I was sitting eating dinner, minding my own business when she came up behind me, put her arms round my shoulders and said,
"Hi, how are you doing?"
"Erm, ok, how are you?"
and so on, until she wandered off, leaving me thoroughly perplexified.

So, what to do? My first instinct was to text/call/ask her to her face "Erm, what was that about, I was under the impression you hated my guts?", but perhaps put slightly more tactfully.
Alternatively, do I leave it alone and see if she makes any more signs of wanting to be friends again?

Suggestions, serious or otherwise, would be appreciated, although in writing this down I'm beginning to realise what a boring and pathetic dilemma this is.

kthx

*Anticipates deafening silence of no one caring*