It depends on how low of a supply she thinks she's going to have. How many oz per feeding did she have to supp last time? You don't want to freeze too much because it would go to waste if she wasn't able to use it. Have you seen the little slim line trays thingys? I pump WAY too much to use them, but they might work for you. You freeze the milk into 1 oz tube thingys and then you put them in a ziplock baggie. You can take them out one at a time or more so you don't waste any milk. The mom that makes them is on here. Firefightermom or something? I can get you the exact name if you'd like.