Has she EVER had an orgasm from oral sex? If not, the issue could be hers and not your technique.
I started dating my wife when she was 16 and she was very naive and inexperienced then. She'd fooled around a bit with a few blokes but nothing too serious.
For ages (a few years I think) she was unable to reach orgasm with me, but now she can. 11 years later, I am able to go down on her and bring her to orgasm within a few minutes if we need to be quick.
She has never had an orgasm from just penetration, she always requires clitoral stimulation be it from tongue or finger.
Talk to her about it, ask if there is something she'd prefer you do. Learn about it together and things should work out for you
