Maybe it is the type of song? I sang my boy a lullaby about how I love him. If you ever want a laugh google the “kitten lady no balls song” it is on her YouTube channel. That kitten was mesmerized by her singing!
A while back, I started saying, "You're such a good girl!" to my Sasha, as I fed and pet her, as well as immediately after she caught her worm of choice during our games of chase. Quite expectedly, this established this chain of words as a conditioned reinforcer ... so much so that when she's waiting for me to prepare her meals (previously an anxious/excitable time) and I say these words, she relaxes, evidenced by lying down and accepting pets.
I'd suggest introducing brief, soft singing (2-3 seconds) while putting down her food bowl during meals. Then, while giving her treats. (Sing at no other times.) As this goes well (no aggression), gradually increase the duration/intensity of singing and pair with play and petting. This is a desensitization strategy that can work quite well.