Have her describe her fantasy as you lick her pussy, even if she pretends that it is only you in the picture... Tell her how it turns you on and makes you hard when you see other guys get hard for her... she loves to tease, I'm sure...
These are non-threatening things for her that she can incorporate into her erotic repertoire, soon she won't even question where the impulse came from to suck other men's cocks (at least in her fantasies).
Once she has accepted these things as a part of her sexuality, you will likely want her to begin 'externalizing' these behaviors, in baby steps, maybe starting out with extra short mini skirts, or tiny wispy G-strings that barely cover her puffy pussy mound, that she can flash discreetly in a restaurant, valet parking, PTA meeting... lol
You get the idea... be sure it is a gradual introduction to these concepts and that she has the time to assimilate their meaning, and how she could fit in to all of this. At ALL times, the fantasy has to be alluring to HER, and never doing something that does against her nature in order to please you. It's merely a matter of shaping these concepts, and framing them as opportunities for her, her sexual fulfillment and growth, and self confidence... lol, right!
Of course, you can't wait to see her bouncing up and down on a stud's big cock... but if you say that right away, you'll spook her...
Let her come to those desires/conclusions based on her own motivations and opportunities to show-off her feminine wiles.