[Vwoolf] How to pronounce "Isa" (Between the Acts)?

[Edward Mendelson]

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Would any native speaker be willing to tell how to pronounce the short form of Isabella Oliver’s name? Is it “Ee-sa” or “Is-sa” or “Eye-sa” or “Iz-za” or something entirely different?

These American ears will be grateful for (mixed metaphor alert) enlightenment.