OMG, London is the most precious thing ever!!! I think she's adorable with her little lion hairstyle.
I have also never heard of internal fleas.
I just googled it and came up with nothing... all I found was internal flea control - which is ingestable items that will repel
external fleas (i.e. garlic).
Maybe she just has slow-growing hair. Did you ask the breeder if her parents/grandparents had normal growing hair?