She is kinda weak right now...she received some nerfs in the previous patches. Also, devourer got nerfed so I wont recommend to play her with devourer. She is a jungler with good presence. I feel like she can carry hard just if she is very ahead. Otherwise, she feels weak. When Rek'sai was released she has insane damage and damage scalling, especially on her E. Now you got a lot of champions that can do way better than her.
To carry with her is kinda hard. Her only cc is a knock up, she isnt very good in teamfights. Back in season 5, she was a trully beast, now she feels more like a secondary support, since the recommended build is a tanky build that contains items like
.
That's just my opinion, feel free to search for some Rek'Sai mains, maybe it will prove that I am wrong.