Wrong month for my birthday on my Green card. What can I do?

My mom has had her green card for 29 years has a clean record. She's from Guatemala, but on her residency card, it shows her being born in February instead of January. She never got it changed because she feared it would be taken away. Now, she wants to get her CItizenship is it going to be a problem? What should she do to get it fixed? Please advice me.