Whilst they are pretty similar I think they sit just on the right side of the 'ok' line! I might be tempted to use coralie (hence giving a difference in the end sounds) for the full name and them you could still use Cora as the nn. Lovely names! Cassia is on our long short list.
Love the name Cassia, almost had it for dd but went with Carrie as don't like 'Cas' but quite similar to Cora? Told friend about using it for ex so she named her daughter Kassia can't explain why but I think it's horrid with z 'K' not that I've said if course!!