Go ahead and give her oral, but stay away from direct clitoral contact. The clitoris is actually a lot larger than the little piece you see sticking out. It branches off around the vulva and extends internally fairly far. (This is why some women find squeezing both outer lips together firmly to be pleasurable.) It also goes back into the body a fair amount, so some women find firm pressure on their mons pubis to be pleasurable too. (The little mound in the front where the pubic hair grows.) You could try licking the area right above her clitoral hood, or just applying pressure there.
If you haven't read the book already, try reading She Comes First.
In it you'll find a thorough explanation of female anatomy, and a technique guide. I think you'll find it invaluable!
I can't stress enough also how important communication is in a situation like this. Ask her what she does to pleasure herself, and then try to emulate that. As you're going ask her if she likes what you're doing, if she'd like more or less stimulation, or if she'd like it in another area. Best wishes!