Based on what you shared, I have some work advice that may help you with this situation. If you are feeling a sense of responsibility for this freelancer’s hire or subsequent poor performance, don’t. Two others made the hiring decision. You offered a solution to your boss to try to salvage the situation, which was a good call. You acknowledged your discovery about LinkedIn, and she continued to hire him for a different role. Not a wise move in my opinion. Now, ironically your boss is allowing the freelancer to do poor quality work, and it sounds like you’re the only one concerned about it.
I’m guessing that while following up on the freelancer you worked more hours in the process, and it may have been stressful too. I understand you want to deliver quality work and keep others happy, but your boss should be stepping up here. It’s too bad she isn’t. I don’t know what your options are other than to just say to hell with it and stay in your lane. If you do that, the boss may come around as the errors pile up, or she may not. Either way, I think your best approach is to step back, stop worrying about it (if you can) and bide your time.