Welcome and congrats on the new arrivals
It sounds like mamma is just a bit too cramped. A two foot box is just not enough room for her to manage her motherly duties. She needs room to stretch out and get comfortable since she will be there for a while and several times through out the day and night nursing her pups. I would suggest getting her and the pups into a larger whelping box. An under bed storage box would make a nice space for her and her growing pups. Plus an open window would not hurt the pups as long as they are being kept warm with a heating pad set the low temp.