When you are having sex, how much foreplay do you do?
The thing she does with pulling away before an orgasm can come from too much tension. How about you try to massage her for an hour or so before sex? Go through her whole body, especially the toes, feet, ties and neck.
Take your time and release all the tension in her body. Light candles and incense (the good stuff, Nag Champa). Make the whole night into a spiritual experience. Let your focus be on relaxing her, not on penetration or orgasms.
There are also videos on how you can give girls amazing orgasms with your hands. Although the tongue feels better, these hand techniques for giving orgasms are much more effective. I recommend learning some of this as well.