YOU SAID:

I have a shitsu up stairs and she pees when she's nervous

INTO JAPANESE

私は階段を上っていて、彼女は緊張しているときにおしっこをする

BACK INTO ENGLISH

I go up the stairs and pee when she is nervous

INTO JAPANESE

彼女は緊張しているとき私は階段とおしっこを上がる

BACK INTO ENGLISH

I go up the stairs and pee when she is nervous