California squatter (no lease) 3 day notice?

[Jeremy Julian]

My grandfather willingly let a friend of a friend move into a studio apartment ADU in his backyard.

It has been a couple of years now and she has piles of junk inside and outside of the unit and has also been throwing food scraps into the yard and into the pool.

I believe her plan was to outlive him and acquire the property through adverse possession.

Long story short, I'd like to hit her with a 3-day notice and start the eviction process ASAP.

Is a 3-day reasonable in this situation, in San Bernardino county California?

Does anyone have resources to a 3-day notice with the proper verbiage for such a case?

I'd hate to make things worse by not speaking lawyer, lol.

Any feedback, ideas or links would be much appreciated!