Question

Mr. Santos is a tenant who has been occupying an apartment owned by Ms. Cruz for several years. Due to financial difficulties, Mr. Santos fell behind on his rent payments for three consecutive months. Ms. Cruz, being understanding of the situation, agreed to waive Mr. Santos' right to pay the accumulated rent in exchange for various household chores and repairs around the apartment.

Meanwhile, Mr. Santos decided to move out after a few months and found a new tenant to take over the apartment. However, when Ms. Cruz learned about this, she insisted that Mr. Santos still owes her the unpaid rent despite their previous agreement.

Can Ms. Cruz demand payment of the accumulated rent from Mr. Santos despite their agreement? Discuss the effect and application of the waiver of rights provision under Article 6 of the Civil Code in this situation.