My personal experience :
I have a lady colleague who is still single but attached, I am
married with children.
We grown close as we do travel on business trip together
before.
We do SMSes each other after work on a daily basis about work, her
bf, my family & other stuffs.
Most weekends, we dun SMS unless related to work.
There's an un-spoken pact between us about our friendship as to
where to draw the line. So far, nothing 'crazy' happened and should
stay that way.
My point is, in your case,
Work on being friends first, dun think so much.
Even if she do likes u, it can mean just that - just friends.
Cheers. 
