I would send her a polite pm saying that you have someone else interested but she has first dibs, and you need to know ASAP.
I recently had someone give the impression they only wanted to trade so I sold to the next person. Turns out she was just trying to feel out what I would take and wanted the item regardless, so I felt bad.
Tashauna~~proud wife to my trained boo-boo fixer and mama to 4 boys on earth (Jordan-01/15/08, Logan-12/16/09, Connor-05/17/11)...and finally our rainbow
Jackson (11/24/13)! and two in heaven ^i^ (10wks-11/12 and 4 weeks 2/13)
and get paid!! I've earned over $1000 just since Jan 1, 2013!!!