I agree she sounds like she is a mini. My Nigerians are about that height. Two cups might be right if you are milking her while also sharing with the kid. Mine can all hold back their milk if they still have kids.
Might also be diet and/or genetics. Some just don't produce as much no matter what you do. She should be getting enough roughage all day to satisfy her. Mine all get alfalfa, but a good quality grass hay can do as well. Mine also get grains while on the milk stand. There is a huge variety of choices for that, so I'd do more research on that and see what works best for you and the area you live. Also make sure she was access to a lot of clean water. If she's dehydrated, she can't produce much milk.