If you're asking about her career then I can't answer because frankly I could not care less about it. Judging from the sperging in the thread it's something to do with abortions.
If you're asking why her death is such a big deal, it's because Ruth declined to retire under Obama because Hillary would be crowned in 2016 and she would be able to retire under the first woman president of the United States, as if that would make any difference in anything whatsoever.
As we all know, Orange Man ruined Hillary's coronation and became president instead. This posed a huge problem for Ruth, because now she couldn't retire or her replacement would be a conservative judge. The only option she had was to live until a Dem president was elected again and then she could retire.
Because of her being the only thing preventing Trump from appointing someone, the left basically deified RBG in the last two years despite nobody knowing about her before that. So the right wanted her to die so Trump could appoint a conservative Justice, and the left wanted her to live until Biden was elected so they could appoint a liberal Justice in her place. That's why her death is so politicized. It's not about her, it's about the Supreme Court.
tl;dr: Ruth refused to retire under Obama, accidentally handed Trump a Supreme Court seat because she was old and couldn't outlive his term.