Oh no, poor little one, HFMD at 6 months is really tough because they can't understand why it hurts so much. Cold milk is the right instinct, and from what I've heard, patience is key, some mums say their babies took almost an hour per feed, just sipping very slowly, so don't panic if each session drags on as long as she is still taking something in. For a formula-fed baby this age, you can actually offer small sips of cooled boiled water in between feeds to help top up her fluids, and my neighbour's PD also suggested trying ice pops made from diluted formula or breast milk to numb the mouth a little before a feed, which made a real difference for her baby. The main red flags to watch are if she goes 6 to 8 hours without a wet diaper, becomes unusually drowsy, or refuses to drink anything at all, at that point it's a trip to the A&E rather than waiting it out. Do check with your own doctor though, especially since she's only 6 months, they can assess properly and may have specific advice for her age and weight.