You will have to keep treating her every month to keep her ( and your home) flea free but how long it takes until all the fleas in the house have either been killed by the spray or pupated and jumped back on the cat depends on the enviroment. So eggs that are in a cool still room that is very rarely used will remain domant until the conditions are right.
I cant quite remember what the vet said about the indorex but I think it was something like it kills the fleas and arrests the development of eggs but dosent effect any that are pupating. There is bound to be a member who will tell me I ve got that the wrong way round but its something like that anyway.
the frontline makes the fleas very active as they are dying so you tend to see them more on the surface of the cats coat. I mention this because if the cat seems clear and then wanders into some place she hasnt been for ages a few may end up on her and if you saw them you might think that she is riddled with fleas and that the treatment isnt working.
Sounds like you are just about on top of it though so stick in there.