Concerns about re-entering the U.S. after obtaining a green card, given a past record of unlawful presence

I’m a U.S. citizen. I have a question about a green card holder’s entry, so I’m reaching out.

5 years ago, my parents were sponsored by me and received their green cards. My mother is now planning to visit Korea this May, and I’d like to know if there would be any problem when she re-enters.

My parents came to the U.S. in 1998 and were out of status, then received their green cards 5 years ago through parent sponsorship — I’m worried there could be an issue when they re-enter the U.S.

My mother has no criminal record and plans to stay in Korea for about 2 months.