Sounds very odd indeed. If she's still strong, and is eating hay and cake, I'd be inclined to leave her until she sees sense! Offer her a bottle whenever you are doing a feed, but don't force her.
I assume you've checked she hasn't got any sores in or around her mouth ? (Orf for instance - we had one terribly badly affected last year, mind it never stopped her guzzling her milk even when all her sores bled when she did so. Poor wee mite.)
Other things - milk temperature, the brand and mix (same brand? same recipe? same water?) Sometimes the silly little things don't even recognise it if it's cooler or warmer than they are used to
