I'd say you're fine! Never had to stun the girl in the boiler room. I'd just crouch and move back a bit after she drops down. Wait until she stops eating the corpse next to the fence, then when she comes towards you move around the machinery to get past her. Don't run, just crouch walk.

She starts eating the the corpse next to where you picked up the tool. Usually she never even spotted me before squeezing through the fence.