depend on ur budget because 11promax is a good phone as well 

text and messenger mostly? 128gb is more than sufficient. Even iphone 12 64gb would be enough. Unless she takes a lot photos of flowers and grandchildren.. better go for 128GB then.

Based on my personal experience and usage patterns, the 11 Pro Max will get me about 60-90 minutes more screen time. Standby times are about the same. And yes 128GB of storage is good enough based on that usage for your mum.

Buy new casing to make the phone looks new, hahaha...
Samsung has a history of motherboard failures

I'm a bit more careful when it comes to influencing folks to switch from Android to iOS coz it can backfire spectacularly in a sense that they might totally hate it. When I was younger and had a bit more energy I would engage endlessly in the iPhone vs Android debates but now I just tend to let that slide, hahaha. Of course I still get some friends asking my opinion coz they know I have a penchant for changing and trying phones but I always ask them two questions: 1. What is your priority in choosing a phone and 2. What is your budget? Then you find they actually end up answering their own question, hahaha...

But of course, in your friend's case it's totally different since she already has an iPhone X as a secondary phone. Gold will look very, very good with a saddle brown leather case