Why did Cal take extra care going over the children's clothes before going to her church in To Kill a Mockingbird?

Although Jem and Scout rarely "dressed up," Calpurnia made
sure that they dressed properly on special occasions. She saw to it that Scout was
wearing her "pink Sunday dress" at the Missionary Circle tea, and she probably made sure
that they were in their Sunday best when they attended their regular church. But Atticus
was out of town on this particular Sunday (in Chapter 12), and she didn't trust them to
go by themselves (ever since the day Jem and Scout helped tie Eunice Ann Simpson to a
chair and left her in the church furnace room). So, when Calpurnia asked Jem and Scout
if they wanted to go to her place of worship--the First Purchase A.M.E. Church in the
Quarters--they were happy to go someplace new. What they didn't realize was that
Calpurnia expected them to look even better than they normally did. She was proud of the
Finch children, and since few or no white people attended her church, she wanted them
looking their best because how they looked would inevitably reflect upon her as well.
Nearly everyone at First Purchase treated the threesome respectfully (except for Lula,
who didn't appreciate white faces at her church), and Jem and Scout gained some valuable
life experience from their visit.