From an ABC affiliate [Interview with mother at the link, and you can see the cake receipt, which does not specify a rainbow design]:
Afterward, the school sent a letter to Kenney's family saying the 15-year-old was being expelled, effective Jan. 6, for "a continued breach of the Whitefield code of conduct, which was discussed in-person on October 17, 2019."
Alford said she also received an email, saying her daughter's behavior "demonstrates a posture of morality and cultural acceptance contrary to that of Whitefield Academy's beliefs." Alford said the daughter's email was in reference to the post on social media, while the school said Kenney violated the student code of conduct numerous times over the past two years.
...The school's code of conduct addresses sexual orientation and notes that a student's off-campus behavior must align with those beliefs or face disciplinary action.
"All parents who enroll their children in our private school know up front that we ask the students to adhere to a lifestyle informed by our Christian beliefs," the school said in a statement.
Whitefield Academy in Kentucky expels student for wearing rainbow shirt, having rainbow cake, family says | abc13.com
From MSN.com:
Jacobson, the Academy's head, says that expulsion came after "two years of continuous violations of our student code of conduct."
"Inaccurate media reports circling stating that the student in question was expelled from our school solely for a social media post," the school said in a statement. "In fact, she has unfortunately violated our student code of conduct numerous times over the past two years."
The school added that Whitefield Academy is accredited by ACSI/AdvaceED and a member of the Non Public School Commission of Kentucky, and therefore we meet all Kentucky regulations and laws. Our code is on pare [sic] with ther private Christian schools in our area. IT is unfortunate that one of the student's parents chose to post internal family matters on social media, and we hope our former student is not adversely affected by what her parents chose to make public about her situation."
Louisville Christian school expelled student over a rainbow cake, family says