It isn't just pinworms that cause this, which is why parasites are often overlooked as a cause if there are no results on the tape. I would treat for parasites, because if she eats meat, chances are she has them regardless.
Medical treatment is albendazole, very effective, but you need a prescription and I personally avoid medications altogether.
Herbal treatment is black walnut hull and wormwood tincture, but it must be constant dosing throughout the day for a couple of weeks.
The best treatment, in my opinion, is MMS (chlorine dioxide). I love this stuff, it treats everything... so any other issues she has will also go away magically - and I do mean everything. I used it with my son when he was a baby and I would use it on a newborn in a heart beat. Very safe, and degrades into sodium chloride when the work is done (table salt). You can get it online, and I can tell you how to dose or you can follow the site of the man who discovered this.
Look around the site on how to dose, but basically, I would start with one drop every hour for a day and then two drops the next day each hour... continue increasing until she is at one drop per 11 pounds of body weight. Watch the poop, it may get runny, full of worms, or she may vomit but these are detox symptoms.
I would treat for parasites and then reevaluate if she is still poking around in there. Although, I like the previous post that suggested offering private time in the bath.