What should a woman who has embraced Islam do about a tattoo that was on her body before she became Muslim?

A tattoo that can only be removed by such an operation does not need to be removed, because that would be difficult and cause pain. Allah Almighty says: (He has not placed upon you in religion any difficulty). Your remorse and dislike for it, and your determination not to repeat this act, are sufficient, and Islam obliterates what came before it.