are you totally on the cable phone now and have no land line? If so, check out virgin mobile. You do have to buy the cell phone (the cheapest is 59.99) but the way it works is that you have to fill up the phone with at least $20 every 90 days. That's it.
Can you introduce her to the neighbors? Maybe if something goes wrong, she can connect thru the neighbors. Plus, by introducing her to them, they'll know she's there and will kind of watch out for her too. We do that here, when we go out on vacation, we let our neighbor know so they can keep a watch and collect the mail for us.