G.T.
She might have a fatty pallet that relaxes when she sleeps thus causing all the vibration. Also could be a deviated septum. Milk causes phlegm, would she take a dash of water before lying down, maybe to clean the milk out of her throat?
I'd have the doc look up her nasals and her throat, it's worrisome when you know they have restricted air flow, and snoring is just that and definitely a symptom that needs to be followed up.