Would that happen without her being present? 

She doesn't want to evict her due to her being her daughter(23) and her daughter has a 3yr old.

Once inside the walls it can simply sheet down the voids on the backside vapor barrier.

The daughter could be on deed for the other 25% as tenant in common.But what is most likely is that the lender will simply have her be a co-applicant on the loan but not have her take title to any of the property. 

Water is now so hot they must be having a steam bath inside the bathroom & I found that the chrome coated shower rod started to rust from so much residual water vapor.

I use a vapor oxidizing system for MH's and rentals to remove smoke smells. 

Plumber recently went down to crawl space to inspect and told resident there needs to be a vapor barrier.

Hello BiggerPockets Community,I'm embarking on an exciting journey to acquire and renovate a duplex from 1900, aiming to tackle the inherent challenges of outdated insulation and the lack of modern vapor and air barriers.

This ^^^ Or just build the little wall and stand it up in place...attach to ceiling and floor, apply vapor barrier and then cement board.

Also need one for retiling bathroom (vapor barrier and cement board).