I don't see the problem. She's tech-savvy on the Ipad, so savviness is not the issue. Some people are just happy with the phones they have.
My SIL's SO uses a flip phone. She bought him a smart phone for his birthday, and it sat unopened and untouched for a few months. She finally returned it.
Right - what's the problem? People seem to be missing this isn't a tech problem (uses her ipad), it's maybe a preference for a simple phone?
And if all you use the phone for is phone calls, I agree that an old flip style is far easier to use - it's a dedicated phone instead of a jack of all trades. Smaller, lighter, close the flip and no worries about damaging the screen. Get a call? Just open the flip to answer - no chasing an icon on the screen that wants to be swiped a certain direction (without 'hinting' at this). I would say the user interface of a flip phone is objectively superior to the UI of a smart phone (for making calls, period, obviously, the smart phone does much more).
OP mentioned the monthly bill, but you can find unlimited talk plans for far less, I'm sure. Pretty sure you can still buy an unlocked basic phone.
Here you go. Ting mobile, just ignore the data, unlimited talk (and text if she does that), just $10 (plus fees.tax)...
$10/mo +$5 per shared GB of fast data
Unlimited talk + text
Nationwide LTE + 5G coverage
Data can be used as hotspot
NOTE: If any data is used at all (and picture/group textx use data), you will be charged the basic $5 data, but that's still $15/month...
And they offer this flip, but she could probably just put a SIM in her current phone...
https://tingmobile.com/shop/tcl-flip_Midnight-Blue-4GB-new-multi-network
-ERD50