Do mezzo sopranos have their own sections in church choir or are they usually kept in the alto sections?

My cousin and I are both in church choir, but her voice frustrates
her. She said she's in between being an alto and soprano, or a
mezzo-soprano for short. She can sing alto fine, but she starts
singing soprano notes sometimes. When she sings soprano, she can't hit
the high notes. Are there such things mezzo-sopranos in church choir?
(PS- NO WEBSITES, JUST ANSWERS!!!!)