Re: Why Does she need so much more?
Do you mean your baby is getting 6-8 ounces in one feeding in the morning and 5-6 ounces in one feeding in the afternoon? If so, that is an inordinately large amount for a breastfed baby to be eating in one sitting. I might start with asking them to break the bottles up into smaller bottles and feed more often, to mimic nursing. Assuming you're gone a full day (8-10 hours) that might not necessarily be too much milk total, but it is definitely too much at once.
How many hours are you at work? The general rule is that your baby needs 1-1.5 ounces per hour mom is away. Most breastfed babies take never take more than 4 maybe 5 ounces max (and that would be only occasionally).
Your pumping output looks pretty good actually, that is a really good amount to get out per pumping session. However 15 minutes is on the short side of duration. If you add in 5-10 minutes per session it might get you another few ounces each. Especially if you're not currently having more than one let down when you pump. Also or instead (again assuming a full work day) you might want to fit in a third session somewhere. On your lunch break, on your commute (it is possible to pump while driving), or at night right after baby goes to bed.
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