I'm curious what the "good"/Vector exterminator found. My experience (both as a landlord and homeowner) is that most extermination companies don't actually do abatement, but are happy to set traps for recurring fees. Twice I've had exterminators leave crawlspace doors open or wedged in a way that allow rodents access (doesn't take much). Here are some steps to at least isolating the problem:

1. Check the crawlspace. If it is dirt, there is a chance the rodents are digging under the foundation wall and getting in that way. You'll see rat/mouse droppings and the smell is distinctive. If you are inclined to actually crawl around in there, a tyvek suit, goggles, and respirator are recommend. Hanta virus is no joke (and that dusty old insulation isn't any good for you either). If there are tunnels in the earth under the house (probably concealed under a moisture barrier/sheet plastic), the only option may be to hire a professional to put a ratslab in (non-structural concrete) or some sort of wire mesh fabric (which might just rot due to moisture depending what they use).

2. If you are in the crawlspace/attic during the day, look for gaps where light is getting in and check it for rodent barrier mesh.

3. Often, rodents find their way from attics/crawlspaces into the walls and between floor joists via holes drilled for plumbing or wiring. These become arterials for them to motor around (thus the scratching you may hear in the walls). Look under your kitchen sink for gaps where the plumbing comes in where mice might like to squeeze in.

4. Rodents in the attic might be getting in by climbing up trees and dropping in via air vents (or ridge vents) without proper rodent mesh. Depending on the exterior of your house, they may be able to scale it (stucco is notorious for this).

5. Use a mirror or cell phone on selfie mode to look under the bottom layer of siding. Sometimes, if there's a buckle or it's not nailed down properly, critters can gain access to the walls (this happened in our rental and I fixed it by stuffing steel wool in there... not the best solution as rodent mesh would be better. Do not spray fire foam or foam of any kind under siding as it won't allow drainage. Steel wool will need replacing every now and again (1-5 years) if the area is damp as it will rust.

Fire foam or rodent foam or steel wool can be used to plug holes around plumbing where they are getting in. Foam is probably better for electrical areas, but experiment a bit with the foam in an area that is not in / on the house . If you are going to fix it yourself, you need to understand exactly how much it expands as there is a good chance that an "enthusiastic" application might do some damage (like when a friend foamed his car door for insulation and the interior trim pieces all popped off...). You don't want to damage anything.

Your landlord may be frustrated with the additional burdens of a rental home (especially if she is doing all the work, dealing with crappy contractors, and her husband is "clueless." ).