It may be flea larvae but I would err on the side of worms here.
If these balls remotely resemble sesame seeds, then she's shedding worm segments. These "sesame seeds" are the dried segments of tapeworm as they detach from the adult worm forming inside the cat.
These will come from her bottom but you don't tend to see them there until the infestation is quite heavy. Normally the first sign your cat needs worming is sesame seeds in her bedding. These may well transfer into her coat as she sleeps and grooms herself which is why you are seeing them there.
If they're like little white rice grains, it's tape worm in it's undried form.
If they're like polystyrene balls, they're polystyrene balls and you've lost a beanbag to providence
Loads of advice on-line about worms, and you can get very good meds on-line (animed or VetUK are excellent, no prescription needed for most standard worm treatments) but your first port of call should be your vet if you've not had her treated for worms in the past, just so he can check she's thriving and advise you on the correct dosage for her weight etc.
PS tapeworm infestation is directly linked to fleas as the flea carries the tapeworm eggs - one naturally leads to the other so if you have treated her fot fleas in the past, it's likely she's been hosting a worm or two since then.
Don't worry - very common problem easily solved.
