I hope your cohort can help! I read this book in the ‘70s. It’s an adventure book – can’t quite recall if it’s only girls or if there are boys, too – and they chant a prayer to the Egyptian cat god, Bast/Bastet… I’ve been trying to remember it for decades!
Lost Classics of Teen Lit: Name That Book! 
The Egypt Game by Zilpha Keatley Snyder? Sorry if you have already considered and rejected this, but it’s from 1967 and has both girls and boys chanting stuff about Egyptian gods, and one of them takes the name Bastet.
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