It seems like the Frontline was washed off, so it might be safe, but I would have to check with my vet before I reapplied it. I have never used it, but there is a medication you can use to immediately kill fleas, but it lasts for only a day. I've heard people here using it cases where a lot of fleas are on their dogs or cats. I attached a link written about it by a veterinarian.
Capstar Flea Medication (Nitenpyram) For Cats and Dogs.