This is mainly changing tile and bathroom vanities/fixtures.

I don’t use inspectors here in Vegas as everything is relatively new with tile roofs, stucco siding and slab foundations.

I have dogs, cats, and horses and have had carpet and hardwood/tile.

If I am assuming this correctly, I don't think the scenario you are laying out would apply to you. 

Make sure whenever you lay a dollar out, you get lotsa dollars back. 

I usually use a piece of 1x2 wood or whatever I have laying around and a screw.

I need help figuring out:- Total cost of rehab/repairs (plus any recommendations for junk/hauling services)- Help estimating current Fair Market Value of the home, before/after repairsI can probably figure out FMV after repairs but basically I'd like to understand what needs to be done to restore the house to good working order and lay out a plan to do so.

Of course if you do not have any siblings and you are her only heir, then these issues would not come into play.Also to add I would be sure you have significant reserves so that you do not face foreclosure on her house due to a lay-off or another significant stressor which could prevent you from making the payments.

Do I simply re-tile downstairs shower or is it worth it to tear out enclosed shower and add a tub/shower as a value add?

Simple electrical and plumbing, trim and drywall work, tiling, etc.