Couple things stand out to me in that pic. First, as previously pointed out, the watch. That's a man's watch. Second, her legs look a bit thick to me for a girl of her stature, so that's questionable. Something about her rack, from that pic, looks a bit off (kinda makes them look fake & most women wouldn't go get small fake breasts).
I second the suggestion to talk to her on the phone a couple times first. Try to make it a lengthy convo so you can really get a feel for her voice. If you talk to her long enough, you should be able to tell if it's a female or not.
Meet up at a Starbux during the day. Not much can go wrong there. If she really is a she, put your signature on it like a pro.
Would be helpful if you posted up a couple more pics.