I have a friend that has a resident card and decided to apply for citizenship. She has not heard back, she is still pending but in the meantime her green card expired. What should she do?

She should get an info pass appointment and get an extension. However, the best thing would have been to do it before the I-90 expired. Nevertheless, she can call the USCIS phone number and schedule an info pass appointment.

I am not an expert or have legal background, but when I was at USCIS office I saw a person get a temporary card to replace the expired card. I would suggest calling the USCIS office and asking them as well as making an appointment.