I know two little sisters named Cora and Lila. I really like Cora, but agree there are too many "k" sounds paired with Katherine.
Cora Margaret
Cora Josephine
Cora Elizabeth
Cora Evelyn
Cora Louise
Cora Juliet
I really love Emma despite its popularity. Other suggestions: Anna, Cara, Olivia, Kate (Katherine), Julia, Mia, Claire