How long can a US greencard holder stay abroad? I've checked the documents that USCIS give out to new residents & it says 1 year, but a recent immigrant told me that during first-time immigrant processing at the airport, the immig officer told them that if they plan to travel abroad after they get their greencards, they have to return within 6 months. My mom is abroad & can't come back till April (her 7th month abroad) due to personal reasons so I want to find out if USCIS will revoke her greencard if she's not here before then.
The answer isn't really as simple as "how long" - overall it isn't a question of time spend abroad by itself; there are other factors, with time abroad being only one part of it.
The question is: what would cause a determination that a person has "abandoned" a green card - a determination made when the person tries to come back to the U.S. based on the officer's determination of the person's subjective intent. This is a fancy way of saying "what the officer thinks you were thinking" with regard to abandoning the green card based on the facts presented, whether or not that was actually what you were thinking.
As a general rule (and this is the only point where time spent abroad can really be a guide, without anything else), if a person is abroad six months or less, they rarely question intent and make a determination of abandonment.
Six months to a year abroad (like your mom), and the person can still be OK if they can prove that they still have very strong ties to the U.S.: property here (real estate or personal property, such as bank accounts, a car, etc.), family living in the U.S., a job to return to, etc. When returning, your mom can bring evidence of her ties to the U.S. - you might want to consult an attorney about her specific situation to discuss ideas for ways to prove this.
If the person is abroad a year or more without returning, there is a presumption that the person meant to abandon. Even here, though, very strong ties to the U.S. can overcome the presumption. If someone knows that they will be out of the U.S. for that long, it's a good idea to apply to a Reentry Permit - essentially, advance permission to stay out a year or more without abandoning the green card - before leaving.