My best friend is a Canadian, she was shocked when she moved to Texas because she did not understand religion and Bible beaters at all! Consequently she is one of the greatest humans I have ever met, and the sole reason I’m raising my child without religion! When She’s old enough to understand it I will introduce it (I am Catholic) and until then I focus on good morals and zero “you’re a sinner and will burn in hell”.
It’s a southern thing. Bubba, Bubby, sis, sissy and sister are super common and we don’t look twice when we hear it with or without the siblings.
when she starts calling her “little mama” then I’d be worried about the sister mom role.