Our doctor suggested it for my son--he's done it several times over the years. I trust our doctor.
I would only use the P73 form by PHP though. I wouldn't use other forms. You want one with the harmful substances removed. I only trust that company. They told me to only use the regular strength with a child. I found dosage pretty easily. It's much lower dose than adults (like once a day for example at young ages, one drop, etc.)
For pinworms we did pinworm medicine. Is there a reason you're opposed to it? The oregano oil is very strong tasting and pinworm med will be much easier (and it's one dose, another dose in a couple of weeks vs. every day of the much stronger/more objectionable oregano oil). And the oregano oil is also antibiotic so it'll wipe out her good bacteria with all the potential effects of that. If you do it treat her like she'e on an antibiotic in terms of frequently dosing heavy duty probiotics at least three hours away from your oregano. I'm a fan of oregano oil in the right form when needed. It's a super heavy hitter or what I consider a "big gun" so I reserve it for stuff that needs that. I don't throw pinworms in that category.