Who was unwelcoming at Calpurnia's church?

Harper Lee's "To Kill A Mockingbird" follows the plight of a white attorney, Atticus Finch, fighting to prove the innocence of a black man accused of rape. The story is told through the eyes of Atticus's daughter, Scout, a smart and resourceful tomboy type. The story deftly and boldly examines racial intolerance in both white and black communities.
In chapter 12, Atticus is forced away on business for two weeks and leaves his children under the care of Calpurnia, their black housekeeper. Calpurnia doesn't trust Scout and her brother, Jem, to attend church on their own because she heard they were engaging in shenanigans with other Sunday School classmates when they should have been in service.
Instead, Calpurnia decides to take them to her all-black church come Sunday. All of the congregants genuinely welcome the children except for one—a tall woman named Lula. (This is Lula's only appearance in the story.) She demands to know why Calpurnia would bring white children with her, and as a result, a confrontation begins to escalate. However, just when it looks as though things might truly get ugly, Reverend Sykes and his congregants step in and drive Lula away prior to starting the service.
This moment emphasizes the fact that racial insensitivity exists in all sorts of places and among all types of people, even those who professed to live tolerant Christian lives, and shows that acceptance and understanding of others can ultimately win out over blind bigotry.