Do you try burping well after the first 2oz? I would advise against lying her flat to drink too, it's a choking hazard to drink in this position and I believe it can potentially cause ear infections. Have you got a bouncy chair for her, or prop her up on a feeding pillow.
The other thing to think about is that babies aren't always going to be the same amount hungry at every feed, so she may only need 2oz at some feeds whereas she needs bigger feeds at other feeds.
What's her behaviour like when she feeds? How is she after the first 2oz?
Laura