My girl has never orgasmed. Ever. She hasn't masturbated and that isn't an option for her - she won't do it.
When I finger her, she likes it but eventually stops it - 'it's too much'. I really believe that she enjoys it, but I don't know how to put it over the top for her.
I spend some time on the clit, but she usually likes it most when I go deep inside and rub quickly.
Any tips? I want it to happen for her.
It sounds more like a psychological issue for her than anything related to what you're physically doing. If she wants you to stop then she doesn't feel comfortable. Maybe you two should sit down and talk about how each of you feel about her being pleasured and what you both actually want to happen.
Read Female Sexual Response in Chick Chat. And accept that one-quarter of all women never experience orgasm. We all seem to be equipped to reach the top but that many never do. There is a relationship between the age we start masturbating and later sexual satisfaction - earlier the better. Most women who are regularly orgasmic learned it first through masturbation but I have had patients in their thirties (one as old as fifty) experience their first orgasm. This often comes with some other change in lifestyle but it shows that we call all learn at any point.
Pressure from you will not help. Orgasm is almost automatic for men but is learned for women. If she chooses not to learn, so be it.