What's her deal..........................…

So we're both girls and in the same work place. She has a boyfriend of many years. The first day we saw each other we locked eyes and we did that on and off the past couple months. It's been 9 months actually. When I am walking away I see her looking at my behind and just kind of looking at my backside. I mean she could just be wondering that I look skinny or seeing if I lost weight because she knows I was sick but it's not the first time she's done it. Is she just trying to compare herself to me or does she like me? She seems a bit nervous around me but it could just be because she knows about my illness I have. I'm not sure if she's into me or just curious as a friend/you know how girls are always comparing to one another.???