The first LW reminds me of those auditioners for American Idol, where their parents swear they sound like angels and the rest of us think they sound like someone stepping on a cat with strep throat. Be happy he only said your voice was "immature".

Oh! the Choir! Years ago I sang in the choir. There was one woman who could not carry a tune, and when she sang she warbbled---not like a bird---like stones beinging turned over in a blender, we said. It was awful! But, any and all were welcomed to the choir. I moved away, and have often wondered what happed to that woman.
Tho I was only 16 and she was an older woman, I am sure she died years ago.

LW1: I can identify with audition nerves. I'm a skilled, experienced singer in groups, but have had a couple of disastrous solo auditions.

Why don't you talk to your choir director? Unless your mother has completely wrecked it for you, there's no harm in explaining your shyness issues, asking the choir director to give you another chance, or even just listen to you sing a few bars under conditions less stressful than a formal audition. If you can't do that, audition again next year, but your mother's inappropriate response only took things from disappointing to terrible. Your father is right.