Currently a crappy sports bar with no cool factor at all which has been operating miserably out of this space for as long as I can remember.

@Brenden MitchumI would suggest that you reiterate your conversations with the seller via email, cc’ing the listing agent so everything is known to all parties and in writing.  

Anyway, we decided on a refundable deposit, proof of it being a "service" animal, and an addendum that she sign and return that basically protects both parties.

My mentor highly recommended against a 50/50 split since he has had issues in the past where both parties had opposite opinions which ended in a stalemate and no action being taken. 

I would like it the benefit both parties but most importantly the best way to benefit her. 

You can find local meetups in your area by going to Network>Events up in the menu bar.

California is a lien theory state... so based upon that, a mortgage or deed of trust executed by one joint tenant would not sever the tenancy unless the property was sold at foreclosure prior to the death of the party who incurred the lien.If the other owners executed the HELOC they would be pledging their own interests as collateral... which I doubt is the intention.

As for everything else I would do one of two things: either split them out into separate topics and discussions or look them up via the search bar.

Post notice of past due rent to get the eviction party started.  

One party can pay it or it can be split between the buyer and seller-spell it out on the contract and get more info from the closing attorney or title company in your area.