My mother has a US green card (permanent residency) and her US home is in California. However, she has lived outside USA the whole of 2021 (1/1/21 - 12/31/21).

On account of possessing a green card, she is filing her Federal tax return for 2021. Does she also have to file her California tax return?

She was also outside the USA the whole of 2020.

Thanks in advance.

Having lived OUTSIDE of California for TWO years, she can legitimately say she has changed domicile away from California.

For this reason, California has lost legal standing to tax her income UNLESS she has maintained a home in the state to which she intends to return.

ATE

Thank you.

My mother maintained a home (and other financial and residential ties) thus domicile in California. She has made travel arrangements to fly back this year after extenuating personal circumstances prevented her international travel in the past 2 years.

Is there a California FTB tax guideline stating filing State tax returns as optional if the person spent the whole tax year outside the country?

NO state in the United States has such guidelines.

If you LIVE in the state, you must declare ALL world-wide income and pay taxes on that income.