She needs to be more worried about egg sacs than live roaches. Egg sacs aren't killed by poison, and they can literally remain in limbo for months or even years before hatching. Worth mentioning too that one drop of soda or a sugary drink can keep a roach alive for six months. There is a huge chance she brought egg sacs with her, and if she did, it is just a matter of time. If she is the type of person who spills things or drops food on the floor, and if she is the type who is dirty or leaves cleaning undone, we will see them soon enough...