it doesn't matter if there's no written agreement, your grandpa can still evict her, but as my colleague stated, you can't just change the locks, you have to sue for unlawful detainer if she doesn't leave.
The 30 day notice, Summons and Complaint need to bel correct, and eviction is a relatively easy process but you have to get everything right so the tenant can't fight it. Please see the guide linked below, or one like it, for a "how to" explanation with forms for evictions.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.