CL83213 phone/answering machine shuts off after 31 minutes

What service is she using and has she tried a known working corded phone to see if the same thing happens?

Thank you, she has Century Link and hasn't tried a corded phone - have suggested that, but doesn't have one available.   She did call them and they said there is nothing wrong with our line.  Okay, maybe they weren't that indignant, but doesn't mean there isn't either.   I did read something since trying to solve this for her that someone else had this issue, but the resolve wasn't posted on their post.  

Have her find a corded phone to borrow or buy a cheap one at Walmart. She needs to prove where the trouble is. 

Hope she can maybe get one from a neighbor possibly - Yes, I know I'm curious for certain! 

Well, here we are today and my darling Joan got the phone I had shipped to her and we did 30 minutes and off it went at that point.   We didn't unplug the answering machine figuring just because it's plugged in it isn't the device being used as communication at this point.   We spoke on the corded phone for the amount of time usually and it clicked off after about 30 minutes.   So there you have it.  Century Link said that it wasn't them when Joan called them afterwards and they did a test from their easy chair (cough, cough!)   So I guess we'll have to see if we can get the real telephone man to show up like in the Meri Wilson song from so long ago! 

You've pretty much proven the trouble is not inside the home. 

Yup.  Now if the company she pays for service were to actually step up...