Might your aunt perhaps become marginally less awful if she had a tiny namesake? It could be worth a try!
I agree that Susanna
(I prefer Susannah
) is a splendid name and well worth using. It's a family name on my DH's side, the middle name of his ghastly grandmother, but given enough daughters I'd have used it for sure - easy for me to say that, I suppose, since the old lady died before we got married.
I don't think Susan
and Susanna(h) are as different as, say, Elizabeth
, but nor do I think it really matters. You could always explain that you liked the name and would have used it even if it wasn't a family name - that should cover you sufficiently!