Young female toilet problems

We have litter trays for our 2 cats,..one is a 5 yo desexed caramel
coloured short-hair male, the other is a little 7 mo non-spaide black
and white short hair female who we keep inside untill she is neutered..

The male is fairly good, and uses the litter most times, but the female
usually takes a dump in the shower recess (like yucksville :-))

We keep the litter clean of stools altho urine tends to soak thru to the
bottom. Having an extra tray didnt do much. Why is she doing this? Is it
something to do with the male leaving his smell in the litter which is
putting her off?\

We started using absorbant shale type litter, as the paper stuff is too
expensive. This occured when she was about 3 months. It didnt seem to
change anything. She took a long while to start using the litter.

\
Thanx for any opinions, Tim