I understand that you want to find out as much as you can before setting up an Echo for your mother.
However, at the price of around $40 for an Echo Dot (even less when on sale), you really ought to get one for yourself and find out as much as you can first hand. After all, you'll be the one setting it up and you'll be the one that will answer all your mother's questions when something doesn't work right. For such a low priced item that can potentially liberate your mother, you'll save yourself a lot of headaches later on if you learn about it with first hand experience.
The Echo is constantly evolving. It's not just set it up one time and it'll work forever. For basic things, it will work forever. But things will change as new features and technologies come about. A year ago, there was no intercom feature, no phone calls, no drop ins, no what time does a particular store open, no whole house music, no voice control of Fire TV, and many more things. And just this week, Alexa can now send SMS/text messages. A year ago, Wemo smart switches did not need a skill to turn on/off lights. Some time a few months ago, things started not to work exactly as expected. There were no announcements, or at least I didn't see any. But all Wemo switches now require a skill to work with many of the new Alexa features (like routines, groups, etc.) If you had installed a Wemo switch for your mom to turn on, say a TV or radio, and then one day it stopped working, you'd be the one that will have the headaches of finding out why. If you had prior knowledge about Alexa skills, how the Wemo app communicates with Alexa, how to reset a Wemo switch, etc. you'd be far better off than to do all these things in the dark.