Breastmilk Feeding

I am exclusive pump mummy.. At night need to warm up the milk for nightfeeding... How mummies resolve the issue of waiting for milk to heat up and baby is crying wailing for milk? I tried preparing and heat up a feed after every feed. But tonight my girl decided to sleep for 6 + hours.. So the milk was on warmer for 6 hours... Safe to drink? Now I worry she will vomit n LS....