Cat deterrent for persistant cat?

My sister-in-law who lives downstairs recently got a cat. I like cats but I am 26+ weeks pregnant and don't want her around me or in my stuff. I tried the essential oil spray on the stairs and she was deterred for a little while but then just ran past it. My sister-in-law went and got one of those ultrasonic cat deterrent radar things but the cat just walks past it like there is nothing there. My sister-in-law doesn't want a gate but I really don't know what else to do. If anyone knows of something that worked to prevent a very persistent cat I, I need some help. It also has to be something that is safe for my baby.