I dont see any good in reading too much into feelings or over-analysing stuff. You just end up getting confused and flustered.

If I were in your shoes I would be a good friend to her, be affectionate without being sleazy, and when she is back from her trip and over her treatment tell her how you feel.

If you dont tell her how you feel she may never know, and you will only regret it.

One thing that makes me think you may be in with a chance though is the birthday plans - wanting to spend her birthday with you says a lot to me.