Legal Question in Landlord & Tenant Law in California

Why would accepting partial rental payment waive the right to the full rent payments? The landlord has been nice so your friend wants to stiff him for the unpaid amount. If her business had had a large profit, would she want to pay him more in monthly rent? So why should the opposite be true? If he had demanded the amount unpaid would she have paid it? So what is the difference in what happened and could have happened?

The landlord is entitled to collect the full amount of the rent due and that includes any late charges. The lease probably also includes a provision for attorney fees to the winning party, which will be the landlord.

Mr. Shers is correct. Your friend has some hope. What your friend can do is request, in writing, that the landlord reduce her monthly rental obligation. If the landlord agrees to reduce her rent officially, make sure she gets a letter in writing signed by the landlord which agrees to modify the lease. Most leases contain a provision that verbal agreements that alter the lease are invalid. All agreements need to be in writing or your friend will be in it deep like Mr. Shers indicated. Let me know if you need help.