I treat her monthly, and 4 or 5 days before the next treatment is due without fail she starts itching and if she sleeps in anyone's bed we get bites. (and woe betide us if I go over 4 weeks between treatments - which in my experience wasn't the case with other cats we've had).
Are we failing to get rid of them in the apparent 3-week break with no fleas?
Is she more susceptible to fleas than any of my other cats have been?
It is noticeably more of a problem since we moved house. Is she consorting with our new hedgehog neighbours and getting them that way?
What could I be doing differently?