First of all, I don't see the point of using
Elsa as a nn for
Ysabel. Why bother? Just name her
Elsa, with
Elsie as a plausible nn, and cut the cackle.
And, secondly, whatever is the point of spelling
Isabel with a Y? It will get very old very quickly, and so will the on-going need to explain. And, with any luck, your child will live longer than you will, and have to do her own explaining.