Ahh,, but the cartons taste different to the powder!
Is this for when you go back to work? If so, you may be ok for her to just have water (and solids I presume) once the ebm you manage to pump runs out each day, also, you may find that when you are at work and not nursing during the day that you will find you are pumping more than you were so it might not be an issue.
I saw a cranial osteopath who said that he had tried all of the formulas and that Hipp Organic was the closest, taste-wise, to breast milk. I know a few people that have used it alongside breast-feeding.
Keep pumping your 3oz a day, you will get better at it, it's a learned skill. Do some relaxation exercises before and during expressing, breathe deep, close your eyes and think about your DD nursing, hold the baby gro she slept in last night to your nose and sniff it, it all sounds silly but it does work! Stash your milk, get as much in the freezer as you can, and it's not selfish to want to go out at all, you are allowed to!!
Ewes I have tried expressing whilst feeding. The only way I can get the let down reflex is if dd is feeding so this is the best way I can express. As soon as the let down 'feeling' goes, so does my milk flow in the breast I am expressing from.
elmoandella, I hadn't thought of the follow on milk so may give it a go.