She doesn't have any other problems. She was first diagnosed (over two years ago) with a fistula in the vulval area - there were two lumps on either side and it was painful to sit at times. She had an operation to deal with one side, as the lump on the other side had at that time subsided. After the op the doctor told her that it was hidredenitis, not a fistula. The side operated on is now OK, but the other side has grown. Sometimes a hard tip appears (like a boil) and a quantity of pus is discharged. There is a constant slight show of pus. She has been on a variety of antibiotics, which don't have any effect.
Many thanks for your very informative reply. I'll pass it on to her.