Flying in any kind of liquid can be difficult, but fear not. First, you’ll need to fill her 3-ounce portion with breast milk to meet TSA regulations. Preferably, it should be placed in a storage bag specifically designed for breastmilk to save space and keep the milk fresh and safe. (Note: Large quantities of ‘medically necessary liquids’, including breast milk, are allowed in carry-on baggage, but may be subject to testing, a test that can severely impact travel plans. There is a possibility.)
Once that’s done, put your collection of fresh or frozen breastmilk bags into a (frozen) freezable lunch box. Sky Pack the entire kit and caboodle in your carry-on in a gallon-sized ziplock bag.
Once through security, make an appointment at the first airport bar or restaurant you find and ask them to fill an empty ziplock bag with ice. Seal the ice bag, put it in a freezer-friendly lunch box with milk, and you’re good to go.
Again, keep in mind that supplies will last longer if packed fresh rather than frozen. However, the aforementioned hack works either way — it’s also worth noting that Arquilla advises keeping breast milk out of checked baggage whenever possible. Devastating!