I don't have any strong evidence for thinking Gwen is psychic, but a series of details I think might indicate that she is, or at least has potential to be. For instance:

- she saw the fairies out of the corner of her eye, when others didn't

- she could perceive Eugene's ghost, though not clearly

- she looks like Gwyneth

- she makes good intuitive guesses, e.g., that Jack knew Estelle in 1944