Just a few ideas that might make it easier for your mom.
1st, Enable the "Wake Up Sound" this way when you mom says "Alexa" she will hear a beep then she can say what she wants. This help with the timing. To enable the Wake Up Sound go to the App and choose the Menu SETTINGS/(Your Device's Name)/SOUNDS/WAKE UP SOUND (Move to ON)
2nd Create a easy to read "cheat sheet" for her.
Example; Alexa, (wait for the beep) What is the weather today?
Alexa, (wait for the beep) Play Pandora
Once she has the timing down she will be a pro. Just make sure that you put on her "cheat sheet" the sorts of things she'd like to do. Let us know how it goes.