Elizabeth Holland - Is she a fake?

From An Historical Survey of the County of Cornwall: To which ..., Volume 2, Part 1  By Charles Sandoe Gilbert

Oliver Carminowe, a person of great note in the time of Richard I], to whom, he had the honor of being lord-chamberlain. He died, (apparently very aged) in 1345, and was buried (together with Elizabeth, his lady, sister of John Holland, duke of Exeter,) in the church of the Grey Friars, at Bodmin, where they were for some time represented in efligy, she with a coronet, and he with his legs across.

But - there was no Duke of Exeter until https://en.wikipedia.org/wiki/John_Holland,_1st_Duke_of_Exeter b 1352, 25 or so years after this Elizabeth died.

Did the antiquarians bite a big one?

Should we merge her into the real wife, Elizabeth de Pomeroy