Simparica and still tons of flea dirt

Female 10 week cockapoo.

I got my puppy on the 21st of December. The previous owners said she received Simparica on the 18th. I have an indoor cat and never had a flea problem, maybe just one or two here and there and she’s not on flea medicine. I’ve recently visited 2 family members houses with my puppy, twice each, and I think she may picked up some hitch hikers along the way. Over a two week span I have found around 10-12 fleas but they have always seemed to appear after visiting the family’s house. She has received numerous dawn baths, her bedding is washed daily, I vacuum and mop daily. This evening I discovered a huge amount of flea dirt between her eyes, deep near her skin. Although I just noticed it, it appears to have been there for quite some time but I found 3 live fleas in that area tonight as well which tells me it’s still a very active area

If these were hitchhikers, they shouldn’t have survived long enough to leave all of this dirt and there shouldn’t have been live fleas there. Right? Every flea I have found has been live and on the medium-bigger size, never small or dead. I’m losing my mind here. The vet advised against any other topical/oral treatment due to her having Simparica in her system still. I have a feeling she never actually received it from the previous owners.. my cat isn’t itching at all, I have not found one flea on her. I’m at a loss here. Anyone experience something similar?