Okay -- dovetailing on what you have stated and stipulating its truth ...
Love is a response to values, and romantic love combines that with physical attraction. Whatever need she might have does not constitute a mortgage on your life. You only owe for obligations (i.e. explicitly contracted debts) and her assertion of debt doesn't constitute anything morally binding. And her threat of force in order to collect an invalid debt IS wrong.
Basically, her self-centric attitudes are at least narcissistic and borderline psychopathic. And the threat of blackmail pretty much clinches the deal she's a psychopath.
The point I am making in a roundabout way is that the character of a girl is her single most important attribute, and if she'd screw up some guy's entire life over 3 hours of her time? She's not someone one should be involved with romantically because its just a matter of time before she applies that underlying attitude to *you*.
Of course, psychopaths are great at hiding their natures. Because we tend to project ourselves, those of us who aren't psychopaths never suspect.
But once it is done?
Well, in MA there is only one precedent for a blackmailed client having his name kept mum under a court order. In general, to handle this criminally and file a complaint, you are going to have to make some uncomfortable admissions that will be public record.
I have seen some people have some degree of success with threatening to do that without having to actually follow through. But if you are going to threaten to file a criminal complaint, you should be willing to follow through otherwise if she calls your bluff you'll be screwed.
Another approach is to stop hobbying, tell everyone she would inform that you USED to hobby a bit and thereby immunize yourself to the disclosure and tell her to pound sand.
It is also possible that this could be handled civilly through a lawyer. Threatening to sue her for the blackmail may have an effect, but how much of an effect depends on her circumstances. And, of course, such a lawsuit would be much more compelling if it were preceded by a successful criminal prosecution.
One thing you might also consider is a peace bond. (Basic explanation here:
http://www.wisegeek.com/what-is-a-peace-bond.htm) You can sometimes get a peace bond ex parte (depends on the state you are in) and violation of it could lead to automatic jailing, much like a restraining order.
If you are good at DIY lawyering, you might also consider obtaining an injunction. In NH, DIY lawyering is pretty easy. Same in GA. But in some other states (like NY) it is more difficult.
Either way -- save those texts!!
What I did while hobbying is I did it in tandem with legitimate funded research on prostitution so I always had a very provably legitimate reason to be in the company of sex workers and even pay them. Everyone around me knew about this research, so some wild allegation would have minimal impact unless accompanied with pretty impressive proof. Probably too late for that now, but that sort of thing is something to consider for the future.