Here's my 0.2 cents -
I I think it would a GREAT idea to get her a Smart Phone as you stated above and have it with the interoperability as you stated. It sounds like it would be a GREAT help to her.
My ONLY suggestion is that you employ some sort of Cyber Security with it all - whether it's some Anti-Virus or some other Cyber Security mechanism that will give her (and you too) a measure of protection.
I am in school RIGHT NOW (ECPI) and have learned of some really nasty stuff out there as far as Malware...Ransomware....you name it. And the perpetrators have moved from just desktop computers and businesses to NOW targeting Smart Phones.
Basically - ANYTHING connected to the Net is vulnerable if you don't have SOME measure of protection. I've learned that this has become even more of a problem with more workers having to operate from home because of Covid and do more things on their Smart Phones.
My personal suggestion to you is to talk to someone smart at say Best Buy or maybe even Geek Squad about your plans. we have a LOT of smart people here on this blog that I'm sure can offer other suggestions, as well.
Include your mother in the discussion too but ONLY as a brief synopsis - just so she'll know that you're trying to apply a level of security for her with these new prospective devices. Don't bore her with the details.
Whatever is set up for her Security-wise WILL be able to operate in the background of whatever she is doing and she won't have to lift a finger to enable it.
My mother is 76 and she has Cox home suite. She does have some security with that and even THEN she still gets spam calls on her phone because the protection doesn't extend to her phone, at least not yet.
She is mindful, thankfully - of the threat, though.
But yeah Smart Phones...Smart TV's....just about anything that connects to "The Internet of Things" is vulnerable so please be careful.
I really believe that what you are doing for your mother is great and helpful and don't worry - the SECURITY of it all is NOT that expensive....I am certain that a tech entity (or even someone HERE on the Blog) can recommend something to you and your mother that can help her but ALSO keep her safe.
Hope this helps.