"Can I just say that I am interested in if she, or anyone for that matter, could be considered Best Actress in a Musical even though she played the role before. Is there a rule about this?"
These days there's no rhyme or reason to what the Tony committee does. She would have a good argument because they allowed Stephen Spinella to be nominated twice for the same character. But I think they justified that by saying that Angels in America was two different plays and that the first time he was nominated for "Featured" and the second time for "Lead". So who knows which way the wind will blow.
If anyone ever tells you that you put too much Parmesan cheese on your pasta, stop talking to them. You don't need that kind of negativity in your life.