My mother bought a new iPhone got home and had no way to charge it!
Just so I understand, where did she go to purchase this device?
She had sold off her old iPhone with cable and original charger (as is usual!)
Not really usual. Most people do not sell or trade in their phones, of those that do, most do not include the cables.
and her Mac doesn't have USB-C. She had to go back to the store and buy a USB-C charger in order to charge her phone that night.
That's a drag. I am shocked that no sales person mentioned the lack of charger to her, given that they always try to sell those even before this was changed. However, I am curious do you think I should have to pay $20 more to prevent this from happening?
Granted the shop should have let her know, but still, this is ridiculous.
Particularly given that I have never seen a clerk in any store sell a phone (from any brand) and not try to sell accessories. Someone should talk to the clerk's manager as they are definitely leaving money on the table (and creating a bad customer experience)!
There should at least be an option to include a charger if you need it (for free!) or change the cable from USB-C to USB-A so it'll fit any chargers you have at home.
Why? What other items should they be required to give you if you need it? You understand that if they offer it (even only to those who request it), it means those to do not need it are subsiding those who do, and that it encourages people to ask for it even if they do not need it as "they already paid for it."
I'm a 12pro user and I don't have any USB-C chargers for my phone... my MBP is the only way I can charge it through the included USB-C cable. Ridiculous.
Again, why is this ridiculous? You can also use the charger from your MacBook Pro, as well as purchase a new one. Given that you have a new enough MacBook Pro that charges using USB-C, you might want to look at getting a multi-port USB C charger that would let you charge both directly.
Also, to be clear, you have had multiple generations of iPhones and you never purchased a second power adapter or USB-A to Lightning cable? You only had the one of each that you presumably sold with your iPhone? Wow, you are the first person I know for whom that is true.