I think it’s better to say that courts, in general, do not like/frown upon non-competes, but they are enforceable…of course, it also depends on the state in question. But, typically, there should be a reasonable limit on length or the non-compete and the area of effect. I believe the onus is on the party claiming rights to the non-compete. The large law firms know very well what is trending in the various states to have a non-compete enforced.
IANAL, but:
As far as I know, in all states, for a contract to be valid, it must entail a legal detriment to both sides. That is, both sides have to give up something. Otherwise, it’s merely an affidavit or a release or something like that.
So, if you signed something saying you give up your right to compete, but you don’t get anything in return, it’s not a contract. I’m not sure exactly what it might be, but it’s not a contract, and thus, isn’t enforceable as a contract. It may be enforceable as something else. It’s not a “non-compete clause to an employment contract” since it wasn’t part of your employment contract. (It may have said “In order to remain as an employee, you must …” which might make it a contract, but as mentioned above, non-compete clauses are rarely enforceable.)
Regardless, since you’re not employed and not earning any income and not engaging in any competitive activity, you can’t possibly be violating a non-compete agreement. Does the letter state any specific behavior of yours that is evidence of violating the agreement? You could simply write back asking for details of evidence of violations, saying that you will seriously consider ceasing any activity that’s in violation. (Don’t promise to do, just promise to consider.) See what you get back. Unless it’s very specific, it’s junk, and you can ignore it. You can’t ignore a subpoena, but chances are small it’ll come to that. BE POLITE and matter-of-fact. Send it certified mail and keep a copy.
The best way to deal with trolls is to be uninteresting. Avoid getting into any pissing contests. Don’t admit any errors. My guess is it’s OK to make a vague general polite apology like “I’m sorry if I’ve offended you or caused you any problems.” but wait for a lawyer to say whether that might backfire. Logic isn’t always applicable when it comes to legal matters!
Does the letter require any reply or specify any actions you must take? If not, ignore it. If it does, figure out if you can comply without yielding anything or admitting anything. (Let us know what it requires, which would help.)
Consider searching your area for pro-bono legal counsel organizations (e.g. “pro bono labor lawyers” and your area). Consider looking for legal advice forums.
If you have no income and no assets, they’d be wasting their time and money to take any action against you (“judgment-proof”, as mentioned above). If you wanted to be a jerk, you could string them along and let her legal bills mount up. But I recommend against that.