Terry is not at all likely to get any help from discrimination laws. This is because there is a logical reason to prefer a woman over a man to play the part of Snow White.
All laws discriminate between people. A law punishing murder discriminates between those who murder and those who do not. This sort of discrimination is obviously allowable because there is a good reason for it. The sort of discrimination that is not legal is the sort that discriminates against some group for no good reason.
In Terry's case, there is a good reason to refuse to hire a man to play Snow White. It is likely that no man could play Snow White as a beautiful young girl the way she is (arguably) supposed to be played. Therefore, discriminating against Terry is logical and will be supported by law.