Blue Tit trapped in nesting box

It looks like my nesting female has trapped a leg in the box....still 2 chicks alive, 9 others have slowly disappeared whilst i was away..... i would say another few days before they are ready. The male brimgs food but i am concerned the female who is trying to fly off for extra food cannot free herself. She was fine yesterday but today she is getting stresseed..... can i open the box to release her