Do I need to give a 30 day or 60 day notice?

[Daniel Trimbach]

Hello BP!  Any help would be really appreciated.  I am going to sell a rental property in Marin County California...I have a tenant who is in the property and might buy the property when it is on the market.  My question/challenge is that her lease expires March 15th and I can give a 30 day notice before Feb 15th because it is less than one year for her tenancy.  However, if she is there for at least a year the lease goes month to month and I must give a 60 day notice.  She is elderly and said she may need 2-3 more weeks to move out.  Can I have her sign an addendum (with a 30 day notice)that allows her to stay longer but gives up her right to a 60 day notice?  Should I do a fixed term lease?  Any ideas, resources, or suggestions would be awesome!  Thanks so much.