I checked 7 names ending with -
ISSA, and there seems to be no system behind it. With
MELISSA and
LARISSA the -SA belongs to the name itself. In the case of
NARCISSA, the A is added. The only hint I found was, that
CLARISSA was a "medevial derivation" of
CLARA - whatever this means.
There are many more names with just -SA at the end - for various reasons.
I don't believe there is an ending -SA that really means anything.
Andy ;—)