Strongid is the only wormer that does pin worms. I had 3 with it this year, although other 6 Completely unaffected.
Remember to treat again 6 weeks later to get any hatched eggs.
I seem to be having the same problem as the op so I spoke to my vet today who says that as so many of us are doing worm counts and many are only worming twice a year with dual purpose wormers pin worms are on the increase as these wormers dont cover them. I was advised that any ivermectin only wormer would sort out the problem, not just one particular brand?
Try having her allergy tested. A horse I had, I thought has sweet-itch for years until I got him allergy tested and turned out it wasn't sweet-itch at all. He was allergic to dust, most grasses and hay mould (REALLY handy for a horse!!). He's itch out the lower half of his mane during the summer and would sometimes come up in a weird rash / welt type thing over his chest/neck. Some days (perhaps when the grasses were at their worst), he would go crazy rolling.