My neighbor lady is 96 bless her heart. She called me yesterday and said she has 10 inches of snow in her driveway and has already fell once. Well I told Miss Johnson carry your cell phone and anytime you slip call me and I will come over and help you up.
Its all about the Caring
Honestly, I think you should tell her to just yell as loud as she can for you to come when she falls. That way she won't be distracted by using a cell phone and miss her step. Would also save her on a phone bill as I'm certain she's on a fixed income.