Your mom is not the tenant. It sounds like she is a guarantor of nonpayment. In that case she has no rights and only liability. In any case, call the landlord and rescind the notice, apologize for your mom's behavior and make it clear that mom is not the tenant and cannot give notice. Most importantly pay the next month's rent immediately (or even early) so that the 30-day notice is ineffective.
When you say "co-signor", is your mom a co-tenant on the lease or a guarantor on the lease?
I suggest you speak with the landlady to ascertain whether the landlady is willing to keep you as a tenant. The decision is really up to the landlady.
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.