cat pee and poop everywhere!!

I have had my adult cat Amelie for about 3 years now. My friend found her outside one day and I took her in. When I first got her she used the litterbox all the time. I then noticed that there would be pee on the floor next to the litterbox. I watched her one day and noticed that she doesn't squat down all the way so pee would spray out of the litterbox. I changed her litter and that still happend. So, I bought a covered litterbox, and yes it still happend. So, I bought a covered litterbox with a swinging door. That seemed to help a little, but then I started to find clothes that were peeed on. Then recentley we started to let a stray in and out, and a little while after we did that I started to find poop in our bathtub and in our bathroom sink, I know for sure its Amelie. I have no clue how to stop this. I try to give her lots of love so she doesn't feel neglected. I find poop in my bathroom sink at least once a day. The wiered thing is Amelie will use her litterbox and for some reason stop. Please help me

Have you had her checked by a vet? One of my cats will often pee next to the litter box when her cystitis (bladder inflammation) is bothering her. Cats with bladder infections and urinary tract disorders often pee on soft things, like clothes too.

If you have taken her to the vet to have her checked, and she's medically healthy, have you tried moving the litter box forward to where she ends up peeing? My coworker's cat would pee where the litter box used to be if it had been moved as little as an inch.

You need to get your kitty to a vet. Please make an appointment on Monday to get her in.

It probably is not a good idea to let the stray in and out because who knows what kind of disease it may bring it. If you are going to keep it, then have it checked by a vet too and vaccinated and fixed if it isn't already.