It only expires in October 2021. Normally it is advised to renew 6 months before it expires, but you should check on USCIS website, I believe I have heard a mention of just having a temporary stamp that can be requested which just extends the GC for months or maybe a year (?). That is for people who are waiting for their new GC or in the process of getting their n400 so they don't have to go through the whole GC renewal.
Either way, if you file your n400 now chances are it could be completed before October anyway. When you have those long 24-30 months processing times it doesn't mean necessarily that's how long you wait. The processing time at my office when I filed was around 14 months. I filed a month before lockdowns. Despite the processing times being about 14 months, originally my case was supposed to be completed just 8 months later in September. Then the lockdown delayed it. Nevertheless my interview is now in just a couple of days. So despite the delay and lockdown, my case didn't even get to the "official processing times" they list. For some it may be (way) longer for some it may be (way) less. The only thing is they are not really required to give you any updates until you get to the stated processing times. Some big offices are notoriously slower. Check the forums. But not everyone is unlucky to wait that long.
Her GC expires not her status. By law you have to renew it. Many choose to apply for citizenship without renewing it then they learn the hard way when they want to travel.
