Strep with negative rapid and culture?

background My 9 and 7 year old were diagnosed with strep throat. positive rapid tests, fever, white spots and miserable! it’s been 8 days since diagnosis and we are done with antibiotics.

Yesterday my two year old starting vomiting and very tired and later crabby. i took her to the walk in after she vomited and she was - for strep, but red throat. temp 99.2. Dr said treat anyway due to exposure. the swab was fast. today they called and said the culture was negative 24 hours later too. with the exposure what’s the likely hood they maybe didn’t get a good swab? should I continue to treat? we did one dose yesterday and no puking and happier.