It just has to occur to her that giving head is something normal and common, something most women as a part of the sex play. From my experience, most who avoid giving blowjobs do so because they feel a psychological barrier to do it, not because it is very difficult to do physically. If you want to be a nice guy, you can ask her for blowjob leading by example. Go down on her. To emphasize watch sex videos where women and men go down on each other before the intercourse, and women also suck penis after the intercourse, which is a very commonly found scenario indeed.
Men are pigs.
Yes, because astounding number of men still are doing very poorly with personal hygiene. Wash your penis and balls thoroughly before offering them for licking, because they do sweat and have stronger or weaker unpleasant smell. Personal hygiene matters highly for all women, also with respect to nail clipping, fresh breath, smell from under-arms and dirty toes. So keep your genitals fresh and appealing if you want them to serve as a lolly-pop. If you really like your partner giving you a blowjob, tell it to her, tell she is the best cock-sucker in the world.