The scientific name for the "tant" is the perineum, and I'm afraid I don't know why she might be experiencing pain there. If she's ever given birth, then she might have sustained some damage to her perineum. Or it could be that by being on top she is stretching it in some way. She should certainly mention it to her gynecologist to make sure that there is nothing else going on.  There could be several reasons why she only has orgasms in the female superior position. One is that in that position, you can touch her clitoris during intercourse, which the male cannot do when he is on top as he needs his arms to hold himself up. Since it is the clitoris that is the seat of a woman's orgasm, this is the most likely explanation. But being on top also allows the woman to control the amount of penetration, and she may need that control to have her orgasm. There might also be some psychological reason and she can only relax sufficiently when she is on top.

The one suggestion I might have that could solve both problems is to engage in intercourse in the side to side position. This would allow you to touch her clitoris during intercourse, so that she could have an orgasm while you are inside her. This position might also cause less stretching of the perineum, which could alleviate her pain.