"I recognize that 4x revenue is a lowball offer and she probably wouldn't take it. But a standard 10x revenue seems way too risky to me in an emerging market of teenagers."

That's a risk of any early stage acquisition. If you're strongly risk averse, you aren't doing this kind of deal. Every tech startup at this early stage has dozens of unpredictable variables, but when you have a strong cash flow, explosive growth, and plenty of users, the value goes way up.