For whatever it's worth, personally I say, "whatever!" People's names are frequently pronounced unconventionally and it is not hard for others to learn. If any Irish folks want to get their panties all wadded up about Sorcha pronounced Sorsha, that's their problem. I'm certain you're not the first parents to name a daughter Sorcha and pronounce it Sorsha. =)
You might like to ask your question on the Facts board as well, since it is a question about the flexibility of Irish pronunciation. Sometimes a slightly different group of people will answer you there.
http://www.behindthename.com/bb/fact