I wonder how many shining examples of - successful people who originally quit something with nothing lined up - it will take before people stop making such naive blanket statements such as this. Does her risk of failure increase by just up and quitting? Oh heck yes, but does that mean it's 100% dumb and irresponsible in every context?

You have one life to live and if you don't love what you're doing (she doesn't) and has the skills to do something else (she probably does) and has the guts to change her situation (she does), then in my opinion, she is making the smart and responsible decision.