This foal should be getting more like 12 qts a day, and good creep feed as well as hay. She should be getting a lot more than she is getting.
She is acting hungry because she is. You aren't even giving her 1/2 of what she needs, and the creep feed should be left for her to eat on and off during the day.
The below from "feeding the orphan foal".
Generally the normal nursing foal will eat 25 to 30 percent of his body weight per day. For the 100 pound foal this works out to 25 to 30 pounds or 12.5 to 15 quarts of milk replacer. The total amount is divided by the number of feedings to determine the amount of milk that should be offered at feeding. This gives you a ball park amount that the foal should be eating but feeding the foal free choice is probably the best. The foal can eat as much as he needs.
Hay and grain should be available for the foal from an early age. Normal foals pick at the dam's food as early as the first week of life. Solid food does not provide adequate nutrition to the foal until he is about 2 to 3 months of age. Milk pellets can be added to the grain to ensure adequate nutrition. Foals can be weaned off the milk replacer around 3 to 4 months of age.
Monitor your foal's weight and growth on a weekly basis. If you have a scale, your foal should gain 2 pounds a day. If you don't have a scale then you can use a weight tape. A weight tape will not give you an accurate weight on your foal but it will allow you to monitor an increase in size and weight. Foals should have a flat back. Their ribs should be easily felt but not visible. The withers should be rounded and the neck and shoulders should blend well into the body. If the foal's backbone, ribs or pelvis are visible, the foal is too thin. You should check with your veterinarian to determine if there is a medical or nutritional problem. http://www.petplace.com/horses/feedi...l-2/page3.aspx