I would first boost mothers confidence that she is doing a great job. She is getting enough (more) then needed. I usually tell my NICU mothers to aim for 25 ounces. So since the mother is over this amount she may be able to skip 1-2 pumping sessions on the 'good' side and get in an extra hour or two of sleep. 
On the affected side I would ask more questions - did they develop normally or equally during puberty and during pregnancy? Did she ever have any kind of injury to that breast - she may have to think really hard about this - for instance back in the days when she was learning to ride a bike she had a bad fall and the handle bar jammed into her breast. That might be stretching it far. Since the baby is to young to be nursing at this time is the baby able to be held at the breast. Maybe she will have a let down when his mouth is on that nipple and it has more to do with a MER. Has she ever had any kind of back injury (neck/cervical) that could have caused some damage to the nerves? Has she has a good recent breast exam - maybe a cyst or lump of some sort blocking output.

Jessica Callahan IBCLC
USA, NC
 

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