a way to kill fleas in your house is to put a metal pie pan with water and dishwashing soap in it on the floor in the middle of the room. Set a lamp next to the pan of soapy water so that it is well lit. in a few hours check. it might be full of fleas. for some reason they jump in it.
my experience with female cats is you have to keep their litter VERY VERY clean or they won't use it all the time.
also, maybe get an extra cat box. some times cats prefer one box per cat. or more.
good luck.
Just got a new kitten. Feeding Purina Kitten Chow now, but would like to switch to something healthier.
Also curious is there is anything that would reduce the litter box odor or not?