Having 8 million You Tube subscribers brings in several hundred-thousand $$ to the family monthly.
You dont make much money off youtube for the videos themselves. You have to attache ads to your videos to make money. According to one website, youtube only pays $3400-$30,000 per million views, basically one time. Once you include the taxes and music lessons, there probably isnt much left over.
She probably makes more money on the Santa Monica boardwalk each weekend. Talented buskers can make $500/day busking.