Maybe she packs and leaves peacefully or maybe she destroys the house.

Don't know your situation, but if you get 10 roofs that need replacing or a combination of high expenditure items simultaneously down the road...lawsuits, someone steals your hvac, tenant destroys your house, lose your job, and this list is truly etc.; then it might be nice to have the option of paying a lesser mortgage.

It is immaterial, other than that person destroyed their credit for 7 years.2) The redemption means your friend can buy the house back, but that can only be done with full payment for the note, plus  fees and any interest.3) You as a third party could approach the bank and offer to buy the property for cash.  

It is recommended to install additional section(s) of 6-mil vapor barrier material OR re-snug/re-set existing material to cover over all exposed soilThere is ACTIVE evidence of more than one kind of wood destroying insect found in the crawl space.

What to make sure to do, what not to do, and if possible, any way to keep them from destroying the house before they finally leave?

If the carpet is destroyed you should know its going to cost x amount of dollars to replace....ect.Now when you want to ask a contractor to come take a lot at a house you can speak their language.

This caused the medical bills to start coming after me and threatened to destroy my credit.

It destroyed 3 units, but only one severely.

Should the tenant claim the landlord changed the locks and removed her property, the landlord could be responsible for all sorts of damages such as lodging fees, replacement of lost / destroyed property, punitive damages, and attorney fees.

Usually destroying a lot of stuff.