In a long-term relationship, when there are no varied stimuli, but we have sex with the same partner, it starts to take longer to become sexually excited. Men might need to get a blowjob to have an erection, and women need more time for the foreplay. However, women's excitement is often neglected since it is not so apparent, and the wall of the vagina is still dry when the penis is inserted into it, so two dry surfaces are rubbing against each other and friction can lead to scars and even vaginal tears. Just try rubbing your wrists together with pressure and at a high speed. I bet that less than a minute is needed to feel as if it was burning. The same thing happens in the vagina, but since it is a moist environment, it is not likely to heal as quickly as your wrist would. And even if the pain will be bearable within a few days, you might not be able to have vaginal sex for a month if you do not want to tear the scar again.
Ibuprofen might be useful to deal with the pain, but if the woman has lost some blood and she feels weak, then she will need to rest, as well. Warm bath, or ice compress may also help with the pain, but if you want quicker recuperation or if you or she is worried about her condition, then she should also see a doctor to get what she needs.