Over long periods of time vapor itself can leave a thin Vegetable Glycerine (VG) residue that is easily removed with a warm wet cloth.

Another option is to have her be a 2nd loan on the property you are planning to buy thus making it part of the transaction. 

The steel, PSI, and vapor barrier will usually not be adequate.

All that oil vapor accumulates on the walls and cabinets, and becomes a sticky mess over time because it's not getting sucked out fast enough.A powerful range hood would solve this issue, but they tend to be loud.

Contributing to this might be that my walls are also spray foam this exaggerates it since the house is very tight other than the small air leaks that are in the insulation.I was told by my contractor and the spray foam contractor that this foam didn’t need a vapor barrier since it dries with a water tight skin on it.

I plan on getting better ventilation, replacing the insulation that has some growth, and replacing the insufficient vapor barrier.

There shouldn't be capital gains but I heard there is 20% withholding due to her being a foreign investor?

There were no vapor barriers in the floor, floorboards were just thrown down without securing them to anything, some of the floor is not even touching the footers.

When moisture is evaporating up though the slab and ultimately through your grout joints you'll get water soluble minerals that are left behind on the surface of the grout, its called "efflorescence", and yes, its very hard to clean.The only ways to avoid this is to check the subfloor with a moisture meter to be sure it's completely dry or installing a vapor barrier over the slab prior to tile. 

Risks: If the government confiscates like they did in the 1930s, paper GLD is vaporized instantly.