Thanks for the advice and hope there's no hard feelings since I hijacked the original thread. Here are some updates: DD8 says she finds choir boring. I saw a girl from her new school with an instrument yesterday and talked to her mother. She says orchestra starts in 4th grade and is twice a week with 10 minutes of practice every day.
So the plan is to try for another year of choir this year and she can switch to orchestra next year. DD seems agreeable to this plan so I think we've avoided a battle of wills. If she starts to act distressed about choir or negative feelings start spilling over to church in general, it'll be time to quit.