It of course was completely for her to comment at all. Justices aren’t supposed to insert themselves into politics or comment publicly on such things, exactly because it can become a conflict, as it has now in this matter.
Via Daily Caller:
Fifty-eight House Republicans signed a letter to Justice Ruth Bader Ginsburg demanding her recusal from the forthcoming travel ban case, given her previous public criticisms of President Donald Trump.
The letter argues that Ginsburg is bound by law to recuse herself in cases where she has a “personal bias or prejudice concerning a party” or from cases where her “impartiality might reasonably be questioned.” The congressmen argue that the justice publicly evinced prejudice towards the president in a series of interviews given at the conclusion of the 2016 term, in which she called the president a “faker” and mused about moving to New Zealand if he prevailed in the general election.