Not necessarily. You should review IRS publication 463, chapter 4.
https://www.irs.gov/pub/irs-pdf/p463.pdf
Transportation is never deductible from her main home to her main workplace, that's commuting and it's not deductible for anyone. If her main place of work is at home, she can deduct transportation to a second location, like the church. If she is the accountant and works from home, then home might be her main place of work and she can deduct mileage to church board meetings. If she is the organist, her main place of work might be the church, in which case mileage is not deductible. Her main place of work might still be your home, for example if she has an organ at home to practice on, and most of her "work" consists of planning and arranging the music and practicing at home and she only goes to church to play on Sundays. But that might be a stretch.
The IRS has guidelines about determining main place of work in publication 463.
