Not many California teens wait til they are 19 to get their driver's license where mass transit is not as easy as NYC (where 'natives' often don't get their drivers license until into their mid 20's, especially if they also attend college in NYC and get jobs in NYC.) If anything it should've been a priority that would allow her mother to spend her time doing other things.
It's not the norm, but it's not as uncommon as some make it out to be. I grew up in the Los Angeles, and a number of my classmates didn't get their driver's licenses until they were 18 or 19, and a few until they were 21. And believe me, we were far from sheltered. Some families didn't want to deal with the financial issues (car payments, insurance, etc.), some families didn't think they're kids were mature enough, and honestly, some kids really didn't care about driving that much. The public transport in LA is much better than it's made out to be, and it's much better now than it was when I was growing up.
It sounds like there are probably a bunch of issues going on in Mirai's life right now. I hope she and her family can make an informed decision for her, and not make any overly hasty decisions. Especially with Carolina Kostner winning Worlds this year at the grand old age of 25, I think that it's way too soon for anyone to tell Mirai that she has to hang up her skates.