The test

It's a two hander in my head. Dad is being pressured to get the test and go on the register (friends family etc). Daughter is respecting his wishes, because is knows. People are judging her as well.

Not 100% happy with the ending that's in my head. She has an accident and that's when the info comes out and they confess to each other.

From your updated description, it seems as if the daughter is the lead character because she is the one with the moral dilemma. (She must break a promise made to her dying mother, but she can't break the promise)

Yep. Badly written. He is the sick one. He is willing to die rather than upset his daughter.

She knows she is adopted, Mum told her when Mum was dying. But she promised Mum she would keep the secret.