Stay off the clitoris for a while, even the nipples, but with your fingers you can go deep into the vagina. They aren't so sensitive there. Be SURE you have plenty of lubrication as most women don't lubricate enough. If she can't come, she needs therapy and it's a lot more complex for a woman than for a man. The most difficult woman for me to work with is one who's never come in her life.
Religious guilt is usually at the root of it.
I had a woman with a religious background in bed who had never come. With oral stimulation she got terribly excited but couldn't make it over the top. That was before I knew the methods I'm presenting to you. Oral stimulation is the most powerful, if she will allow it, as there is never a lubrication problem. You work out what works best for you and your partner.