RFE = Request For Evidence.
BTW, my mom also extended her stay many times before, never overstayed until this time since my citizenship application got delayed for so long, by the time we filed her greencard application, she is out of status since we didn't file an extension for her. Fortunately, her greencard interview went well and the officer never asked any questions related to this. I don't think that you have anything to worry about, but do reply the RFE and state your facts. Good luck.
