I am pretty sure that
Susanna is the historical spelling. To me, it also looks prettier. The h just looks like it was added on. I just looked at this site
http://www.guildofstmichael.org/guild/names.html to make sure. I can see the cross between
Susan and
Hannah.
Susanna looks more like it was made not a cross between
Susan and
Anna to me. I do not think that sould turn you off though.