Does she really, really have to have a voice-phone? (size, spends most time in voice calls).
An iPad with a cellular radio is something to think about.
Seems like to seniors a smartphone doesn't get much use because of the small screen, fonts, and keyboard,
but an iPad gets used more for reading books, looking up things on websites, looking at photos of
family.
In a newer car, she could still pair an iPad to the Car, and use it the same way a iPhone would
be used.