"Should I address a gap in my cover letter, or would that detract from my strengths?"
No. I don't think you need to address the gap in your cover letter. Let the law firm ask about it in person, and the benefit of having them ask about it in person is that if the person asks about it in person, a lot of times they already like you. And, if you go in there and they meet you and they like you then it's not really gonna be an issue for them. I would not address the gap in your cover letter. Saying that you moved because of COVID, or you were sick, is just really creating kind of issues, and you don't need to do that. So that's how I would do it. Now, as a recruiter, I always do address gaps in the resume usually. But you don't necessarily need to do it yourself, because you're drawing attention to it in the cover letter.