I wouldn't think Letters of Marque wouldn't be all that difficult to acquire. It's a "Win-win" situation for both parties. The local governor doesn't have to worry about that particular ship ever attacking his nation's vessels. (If the pirate was crazy enough to do so he'd be quite readily marked for a particular nasty vengeance and she'd never be able to acquire a letter of marque from anyone else. Who would trust her?) In return, you cause trouble with another rival nation.
Yes, decidedly "win-win".
Yes, decidedly "win-win".