Imo this can potentially be a bit creepy and back-handed if you aren't careful with it...Just relax and draw her picture.

I draw (pretty well). I always take a sketch pad on my travels. I find all this kinda stuff works better overseas than it does in the UK. Maybe it's do with our miserable weather, no one wants to stand and pose in the rain right?

-Do a few warm up sketches that involve looking directly at her and never down to your pad. Also never take your pen off the bad for these sketches. Call these 'warm up' sketches. They actually do help losen you up. And also if you can find an excuse to stare into her eyes like this but don't do it in a creepy way, chances are she'll get hot and bothered and attracted to you. The drawings will look really weird and expressive, but if you re half decent (which I guess you are, they will capture the essence of the person in a way can be abstract and visually interesting), Also it can kinda disarm her. Since you aren't just trying to draw a photo of her but to capture something more that's deeper within.

-Close your eyes and touch her face like that blind girl in that Leonel Richie vid does. Literally feel your way around the shape of her face. Just ask persmission first of course. This can be intense as fuck for her if you do it right. Just do this confidently and softly. (Imagine your hands are auditioning for the right to touch the rest of her). Remember it's about one of the only instance in which you can get away with touching someone's face like this. And it does actually help with capturing the shape of the face in drawing to boot.

-Don't make a big deal out of it. Condition yourself to think of her as 'just' a model, remember she's just a resource that you are making use of. That's it. If she wants to be anything more than that in your eyes she'd better start trying to demonstate her 'other' values and qualities to you. And she will.

-I'd say don't pay her any compliments at all. It goes without saying that she has some kind of attraction value to be worthy of drawing in the first place, don't over egg the pudding. If you have to comment on her appearance, make observations, that are neither posetive or negative stuff like 'you do really have a wide gap between your ear and your eye don't you?'. just like you would about the architecture of an old church you are sketching or whatever. Since she's the same, just another subject, till she proves herself otherwise (if she wants to).

-Don't expect anything. Doing this is it's own reward. And if you go into it with that mindset you'll be more likely to provoke her into wanting you to see her in a different more sexual/sensual light...she' ll want to NOT be just another one of your models.

Just my two cents.

Good luck with this one mate. I'd love to see the sketches too