Doesn't it depend on which language you're using? Nobody would say 'PAris' in a French sentence except as a joke, just as saying 'pa-Ree' in an English sentence would be, let's say, odd. And if you knew that an
Isabel was Spanish, then you'd ask which pronunciation she preferred: I know an Austrian woman who answers to both
Ruth (rooth) and
Rut (Root), but she says it divides pretty consistently according to whether English or
German is being spoken.
But, as far as OP's question is concerned, if she wants to use
Elsa as a nn, then
Isabel (with a Z sound) seems like the only reasonable route to take.