They have different litter boxes and they use them accordingly :)). Maybe she is just worried about his negligence:). Whenever she does this, she does not even enter his litterbox, she just do it from outside of the litterbox.
Hello, everyone. I have two cats a younger female (16yo, 5,4 kg) and an older male (20yo, 5,6kg). They both came from different households, they met into my house. They did not like each other in the beginning, the female was the one who always spit and hissed, attached him and blocked his way...