I said to her that she shall wait so i can sneak behind a dude.. Then i complited the quest and fast traveled away and i don't know where i left her-.-! So what to do?

Check your secret six dungeon first. If she's not there, she's escaped. :c

(Tried fast traveling? That might fix it)

~ Ah, I see you did fast travel. Try sleeping, fast traveling again, retracing your steps. I don't know how long she'll stand in one place.

I guess a dumb question what is a secret six dungeon.. Btw i never bougt a house or else!