Know anyone with a ferret? dont they try to hunt snakes like mongoose's do?

I know it sounds far fetched but I dont know what else to say that hasnt been suggested already, except maybe crush a rat skull and spread its brains all over a heat pad and place the dead rat on the pad in the same area you think she may have gotten into the wall, maybe the smell of rotting carrion and rat brains will attract her, especially with the heat enhancing the smell... Snakes eat alot of carrion in the wild, maybe this will work, my blood python loves to eat his rats after 12 hours of them sitting there...

If it was me I would be considering breaking the walls down and then dissapearing before the landlord showed up. I am so sorry yer little buddy is missing like this, good luck!