[me]

Oregano wont burn if you add it to lots of honey 
And you can use it topically while nursing as well as taking a supplement like oregaresp. I take that and i am nursing. I also take bentonite clay (theres a sticky here that i shamelessly gush on and on about it but i first really started taking it because i was pregnant and the family had parasites  )

You really should first try and figure out if it really is a parasite and what type exactly it is before you start giving things. You dont want to give something that for a particular parasite it will only kill the adults and not the eggs or vise versa. because then you see a difference but it will either return or return in a different way with a vengence. Like eczema. you dont keep covering it with emollients or you could just wind up eczema free but with asthma. kwim?

ETA: or you could all just go crazy with green papaya! supplements if they wont eat it. papaya is something that is wonderful for nursing moms as well as those that arent as far as breast health.
If you do give a herbal remedy be sure it has three things. wormood, cloves, and green hull walnut.
Even better is if you can also match any symptoms with a homeopathic remedy at the same time. and adjust the homeopathic remedy accordingly if you see symptoms change.

Parasites are notorious hiders and have had centuries to evolve. They arent always easy to completely get them entirely out, especially if there are gi issues. they might actually be causing some or all of the gi issues.
Personally, i would work on healing her gi issues so her body can rid them naturally and at its own pace. they cause damage internally that needs to be healed when there are gi issues existing. figuring out why she is having gi problems is probably gonna be the key for you in completely getting rid of any problems. including the nail biting believe it or not.
if she has a healthy gut and you have a diet that aids this like lots of onions, garlic, oregano, citrus, cloves, healthy fats, etc.. then she can come in contact with a gazillion parasites and they will pass right through. because thats what normally happens to everyone. parasites are nasty buggers but they are natures clean up crew that can sometimes go wrong 
which ever path you choose with this just be careful which you choose because you wouldnt want to give something that might end up making things worse. Like choosing an herb that kills the adult but not the eggs and the parasite in particular happens to be one that releases eggs when it dies. then things might appear better for a time but will come back with a vengeance once those eggs mature. or there are some parasites that you want to actually take an herb to stun them along with something to quickly pass them so it will be passed before it has time to lodge its head in and only pass the tail end of itself. i know, but something i think should be said. you dont want to mess around with this sort of stuff when it is a child with gi problems