Sorry I wasn't brave enough to post this in AIBU!
I was round my sisters earlier, her DD is 6wo and was 4.5 weeks prem. Her first feed whilst I was there she opened a carton of formula for her and put the other half a carton in the fridge. For her next feed 3 hours later she poured the rest of the carton in a bottle for her. She then swirled the milk around in the bottle in her hand to warm it literally a couple of times before feeding to her DD. I was 
Is this acceptable to give a 6wo fridge-cold milk? I didn't think so and certainly didn't with DS. My sister is great but has a very fiery temper and I daresay would not have appreciated being told how to feed her DD!
The only trouble is I feel like a letdown because I should have said something.