RBG has always been a fan of abortion rights via incorporating the privileges and immunities clause of the 14th Amendment to the states, a path blocked after the 19th century Slaughterhouse cases. Reva Siegel at Yale Law School is good to read about this.
*privileges or immunities clause, sorry (Not to confuse this with Article IV of the Constitution). And I guess RBG wants to use the equal protection clause directly.