Yes, Ruth Bader Ginsberg is allowed to make comments against Donald Trump. She is an American citizen and is entitled to freedom of speech. Should Ginsberg's political views supersede her professional accordance in upholding the law and the best interests of the United States, her freedom to make comments against a presidential candidate could become problematic.
I do not know who Ruth Bader Ginsberg is, but I think it is more than appropriate that anyone should made comments against Donald Trump. If he ends up becoming president, we - as a species - are going to be in a lot of hot water. He is a disgrace of a person, and should never be allowed the kind of power he is striving for.
Yes, it was appropriate for Ruth Bader Ginsberg to make comments against Trump. Her comments do not interfere with her ability to do her job, which is only to decide whether something is unconstitutional or not. As a person, she has a right to share her opinions about matters that may affect her and those around her.
It was completely inappropriate for Ruth Bader Ginsberg to make comments against Donald Trump. It would be inappropriate if it was for or against any candidate. Ginsberg's job is to uphold the Constitution and remain neutral and unbiased. She is proven that she is incapable of this by her rants against Trump.