1 of my 9 felines pees and poops in my bathroom next to my toilet!

1 of my 9 felines pees and poops in my bathroom next to my toilet!

My litter box gets cleaned 5 times a day or more depends on how much my kitts and katts eat. This has been going on for about 3 weeks. I use vinegar and water to neutralize the amonia smell then i clean with lysol. How in the world am i going to stop her from doing this ? E-mail me if you think you have a solution please!Meeeooowww you very much!