If there's no child with her, then I would doubt they'd let her take it. When I flew with a bottle of breastmilk, I remember reading online first that they would allow a 'reasonable amount' for your flight. ie: One or two bottles for a 3-4 hour flight. If I were you, I'd get some dry ice and a small ice chest for your milk. You may have to buy dry ice a couple of times. OR dump the milk (I know, hard to do. It's like liquid gold!) But I honestly don't think TSA will let her thru with it.
Another idea: Perhaps she can CHECK the cooler with dry ice. Call the airline and ask if that's allowed. That'd be the best way. I think my FIL brought us frozen fish that way -- he packed the cooler inside his suitcase with the frozen fish and dry ice inside.