Nonnie for grandma

So my husband and I are different nationalities and we have lots of variation in language.

His mom has just announced that she will be called nonnie by our child. This is the first time Ive heard this. I googled and it came up with Italian (but she had no history or influence from Italians- she’s from Alabama and a devout American) ..

Is this a southern American thing?

I’m british and it feels so weird to me .

‘What a nonnie’ or nonce come to mind. If it was an Italian thing I’d be completely accepting but I’m going to struggle calling her this with a straight face if I don’t understand where it’s come from!