Okay so she still killed him, just not in the specific way Palpatine wanted. So she won on a technicality. Not really a huge victory for her character though is it?
Failure would have been using the dark side or becoming a Sith, etc. Jedi’s are not pacifists. They all make their own personal handheld decapitation machine. So yes, melting Palpatine’s face off, accomplishing something even Yoda could not do, that’s a huge victory for her character. From scavenger to savior of the Jedi Order.
Except for the fact, that he died before, so killing him again doesn’t have much of an impact anymore, and there’s nothing in the film, that suggests he can’t come back again. Also, had Rey not confronted him, and just joined the space battle, his fleet would still have been destroyed, and Ben Solo would be redeemed, and still be alive. Once Palps fleet had been destroyed, they could have just bombed the Sith Temple to kingdom come.