I completely agree with YourEternalRest. You answered it your self, ask her for number and get to know her over the phone. Being in different schools isn't too much of a problem. Me and my current GF where and still are going to different schools. It works out pretty good in my opinion.
You could also ask your co-workers if they think if she still likes you. Or you could have them ask her for you if that is an option. I highly recommend this if you are comfortable with it.
Let me give you this for warning though. If you are going to date her and shes from work there is possibly going to be things that are going to bug you. It happens to me here and there and they can be terrible. You also may be over protective I don't really know but I'm just letting you know ahead of time before things arise.
All in all good luck.
