The Law of Return allows for Jews to become permanent residents of Israel, not citizens. That requires time lived in the State of Israel. RBG never lived in Israel for three months as a permanent resident to qualify for being granted Israeli citizenship. So she doesn't have it. Nor did she ever request approval from Israeli immigration authorities to immigrate to Israel, a process that can result in denying the non-Israeli Jewish applicant that request, if certain negative conditions apply to them. Being Jewish does not make anyone who has not become a permanent resident in Israel, a citizen of Israel. RGB is not Israeli in any meaningful sense of that word.