What is just cause to terminate a contract of promise to sell a property?

Question

My mother, in Puerto Rico, was evicted from a house she rented, and she promised her property to a tenant with a promise of sale, but my mother, 83 years old, needs it to live in. Can her eviction and her age be just cause for not selling the property and recovering it? Additionally, the tenant demolished a pantry and cement counter in the kitchen of the property and although the contract says that she cannot make those improvements without my mother's express consent, the tenant made them and then told my mother. My mother did not say anything to her at the time, to avoid confrontation, and because she felt that the damage had been done, but after a while, he let her know and the tenant didn't say anything about it. Could this be substance to void the lease with promise of sale contract? 
 
Thanks for any advice you can give me.

Rafael Pagan-Colon · Answer

In principle, destructing parts of a leased real estate property, especially if the rental contract has a clause against it, may be grounds for cancelling a lease and evicting the tenant. Your question does not state whether the tenant is the person with whom your mother signed the contract promise to sell. I suggest that you revise what I'm assuming is a sales contract with lease agreement, to verify what faculties your mother granted to the tenant/buyer-apparent. 
     The fact that your mother is an elderly person recently evicted with no place to go is another weighted reason to renege on the sale. Another possibility is the options term granted to the tenant. If the term has elapsed and the tenant has not executed his/her option, your mother may be liberated from continuing with the sale. 
     Before making any decisions, you should read the sales option/lease agreement to view its terms and clauses, then consult legal counsel.

Q: What is just cause to terminate a contract of promise to sell a property?