Ladies is it a bad idea to respond to this girl?

A year ago I met this gorgeous girl on an airplane going to new york city and she lives there but said she would be going back to Chicago (where i live) for her graduate program. She said shes barely seen Chicago and I told her that I would be glad to show her around when she comes back. Well since then I've gotten a gf but last night I got a call from this girl and she left a voicemail asking if she could take me up on my offer. I want to tell her I'm with someone now and it prob not a good idea but I also am not sure if she interpreted any potential romance or fling intentions a year ago so I don't want to make it more than it's not either. What should I do? Should I just not contact her at all?