jlensbo-
In addition to cell phone you may want to give her some more options. For instance, you could set up another service on the computer via softphone that gives you another incoming number (and very inexpensive outgoing in a pinch.) I use STANAPHONE on a laptop with a USB phone and it is getting regular use in our house. The free numbers they give out are NY area numbers, and one area code happens to be her only siblings' (brother plus wife and 2 kids) area code. So, they now call her using a local number (845 area code,) call quality is the same as POTS and the SR phone is still free to make outgoing calls on for someone else in the family. Best of all, incoming is absolutely free.
I find that a very adequate backup situation.
I did not have to make or receive calls the other night, but yesterday I tried to call my wife and the short outage that happened (after 3 PM) gave me a busy signal. I called the STANAPHONE number and she answered. She didn't know there was an outage on the SR line, but I told her I was on my way to my next client and then called SR's 1-800 #. By the time I talked to a CSR the outage was over with (I guess it must have been a 20-minute thing or so.) I asked about the outage from the night before and was told that SR was putting in new servers and switches and something went wrong. Now, keep in mind that CS (Level 1) is handled by an outsourced outfit, CallTech, so I am not sure if they know exactly what is going on over at SR. I was pressing to find out whether the failover issue was the reason that new equipment is being installed, but the CS just said that they were not being told, that SR has been "secretive" about what exactly led to that nights outage, whatever that means.