I'm not sure the exact prononciation, but I guess "아이쉬아" because 'sch' is pronounced as 쉬.

My turn! "애이시아" That's if the "ai" is pronounced "ey" as in "they". If it's pronounced like "eye" then it'd be "아이시아". It's always a rough approximation. My common name has about 3 possible spellings in Korean.

If it is pronounced as in french, it should be 아이샤

i think 아이자 is as close as you will get, depending on how Aischa is pronounced.