HI!
The first thing I would tell a patient of mine to try is a very good lubricant--Replens is a good brand. I would also tell her to make sure that there is plenty of foreplay so that she is "ready" when intercourse begins. Sometimes if the woman is not fully aroused, there is not enough lubrication, and sex may feel like sand paper. Some women even have bleeding. If that didn't help, I might try an estrogen or progesterone supplement.
I have also seen this problem associated with long term use of birth control pills, so I would tell her to stop those, if she was using them.
Hope this helps!
Dr B