I've worked with people like you are describing and now I generally don't say anything if they don't say 'hello' back. There have been a few who I quit saying 'good morning' to after some time - I just accepted who they were or eventually saw they were not someone I wanted to be involved with ... but there was a time when I did take it personally and wondered if it I was the problem. After all, it is human to want love and validation.

You might want to examine your motives if you are thinking of challenging your co-worker's lack of enthusiasm ... maybe you are wanting to change her or 'fix' her and maybe it really is about your own discomfort. Just thinking out loud ...