@MacKenzie Clinton
There is an enormous amount of panic and fear about mold and mold remediation in real estate these days.
Here's a Wikipedia article to ease your worries about evil black toxic mold: https://en.wikipedia.org/wiki/Stachybotrys
It's perfectly possible there's mold behind the bed for some crazy reason that's the tenant's fault, although highly unlikely in just 5 months of occupation. Here's what I think is the most likely scenario.
There's a chance that on the other side of the wall there's a bathroom, particularly a tub/shower combo, and water's leaking from there and causing the mold. That would be a real problem and require some serious remediation. Post again with pictures if that's what's up.
Here are two others
It may be a small or spraying leak in water supply piping. It happens.
You may find a plumbing vent pipe in that wall that leads to the roof. The vent might not be properly collared. I've seen vent pipes leak in rainstorms.
If, however, you don't find plumbing pipes in that wall or there's no tub on the other side, just replace the regular drywall with slightly more expensive purpleboard, prime with PVA primer and fortify the paint you use over that with a mildewcide additive. If mold forms again on that wall in that area, something seriously weird is happening. That's when you break out the addendums and whatnot and start lecturing about furniture placement. That will probably never happen, though, because you have a fire situation on your hands now.
"The appalling dirtiness of the oven and stove..." Welcome to landlording! But again, in five months they've turned the clean range into a fire trap? That's a lot of ugly, sloppy cooking. I suppose it IS possible, but highly unlikely. In any case, if that's what happened, when you open the oven you should see quite a bit of black carbon sitting on the bottom. Get pictures of it if you see it.
Here's what I recommend for tomorrow: you are going into a conflict-laden solution. You've obviously made up your mind that this tenant is crazy. The tenant might honestly feel that you put shoddy/cheap/dangerous equipment into your rental. DO NOT GET OFFENDED. Take lots and lots of pictures, listen to everyone's stories, say nothing, DO NOT DISCUSS HYPOTHETICALS (Well, if it'sour fault, we'll..."), walk away and plan your next move. Definitely get that FD report.
The tenant is probably going to want some certainty out of this mess tomorrow more than you are. Do not give it. You need to investigate this. The tenant might scream bloody murder about the place being uninhabitable. She will quite probably tell you that she was only doing what your property manager told her to do, so none of this is her fault and YOU ARE RESPONSIBLE FOR ALL OF IT. That's her narrative so far.
You are not going to pay for lodging elsewhere, or promise to make restitution if it turns out that the oven burnt up because of your negligence (that's one of the hypotheticals you won't discuss). Your tenant can go stay with a friend or with a relative for a few days if she feels she has to. She doesn't have any friends or relatives? There's nothing you can do "right now."
And walk away. Don't promise to call.