Pinworms themselves can be seen. They look like small white bits of very fine thread but they’re shy critters the wriggle back in when disturbed, so the best time to see them is after the baby has been sleeping quietly for a time, then take off the diaper quickly and spread the butt cheeks and go in for a look.
Good idea with the poop smear kit. I hope the labs are reliable.
Is she itching almost unbearably? The itch is usually from a pinworm infection but the oral treatment must be given to the whole household and everything has to be treated to stop reinfection from happening, because the eggs are invisible to the naked eye and can drop in clothes, towels, bedding, diaper changing area and absolutely anything the family comes into contact with.
Is she having regular poos and eating well? Is she running a fever or look yellow-ish in her skin or eyes? Do you use creams or powders on her bottom?
Can you stop using your regular brand of diapers for a while, and perhaps try cloth for a short period and don’t use any creams or powders for a while? If the weather is nice, take her out and let her bottom air for a while and see if she picks or scratches at it and cries as she does so.
If she’s been eating and pooping regularly and not running any fever I’d make major changes to her diaper routine for a few days and try to see if it goes away. Lotions and powders can look pretty funky after being smooshed between the hot butt cheeks of a bouncy baby. Lotions and powders can also contain loads of stuff kids develop allergies to.
If your child is experiencing any discomfort, loss of appetite or sleep, exhibiting signs of distress, take her to the doctor or family clinic as soon as you can. If this is just something funky you see in her diaper… change your diapering routine for a day and see if it goes away.