A 3-sided structure is actually better for what you are wanting to help with and get done.
A skilled person behind the controls of tractor or skid-steer will easily scrape and remove the accumulated mess.
Would be so much easier to replace clean dirt for the heavily soiled mess needing extraction.
A mice infestation can be a issue for you too at your home.
Keep vigilant about it.
And honestly, if the home is that infested it needs professional fumigation to rid the problem and not send it out to the neighbors.
Mice can be carriers of terrible disease...
I don't know about signs or symptoms of bites and onset of disease complications but that is just gross...
Is the person also a hoarder inside the house of just everything?
I've seen on TV homes such as this condemned by authorities.
How very sad....just sad.
If this person called 911 then authorities have been inside and paperwork may already be started in the system for her to get help cleaning and clearing the house as evidence of a serious, very serious rodent problem is hard to hide...smell alone would be near overwhelming to those who do not live in close proximity to it and get acclimated some to the stink.
Mice, filth from mice is a particular stench.