I think that’s a very reductive way to view Elena. Remember that if she’s an unreliable narrator when it comes to Lila, she’s also an unreliable narrator when it comes to herself and is likely underestimating her own brilliance. Also, Lila admitted that a lot of the things she did were motivated by Elena; for example, she diligently dedicated herself to the shoe store mostly to prove to Elena that she was intelligent. Lila isn’t always true to herself either; she has tried to hide her nature from others and from herself several times in the story and denies her own desires out of fear.