Appropriate Size for Brumation box?

[SilasBannook]

Hey team. I am brumating 4 of my larger garters--2 radixes and 2 wandering. One of the radixes and both of the wandering are taking to my set up really well. My biggest snake-Big Mama-not so much. Big Mama is 28" long and has been barely eating for a month and a half and totally ignoring all of her food since December 24th. I put her into the same boxes I put together for my other snakes and she just ended up pushing a lot of her substrate into the water dish in her container. I went to clear out the water dish after the third day and when she crawled out of the box she took up a striking position with me and for five minutes I watched her display quite a bit of anger. She has never once lashed out at me so I know she was quite unhappy with being in that box. The box I used is 12" long and 8" wide and 3" high. Given her size should I have her in a bigger container? Below are pics of her container in particular and the other snakes happily in theirs. Currently I have her out of the room I am brumating the other snakes and have her back in her tank where she is back to being her normal nice but still not eating self.

Big Mama sizing pic 12_15_12.jpgBig Mama messed up box 1_2012.jpgFlamestrike Brumation 1_2012.jpgIsis Brumation 1_2012.jpg
Pic 1: Big Mama in sizing picture in container (not her brumation box) with 6" ruler
Pic 2: Big Mama's messed up brumation box with substrate in water dish
Pic 3: Big Mama's bo, Flamestrike (23") comfortably staying in his box
Pic 4: Wandering garter Isis (16") in her box

I had the heat pads turned off for the past few months. I am starting all of the snakes out in these boxes in a cupboard where the temp is around 55^o for a week before I move them to the floor where the temp ranges from 45^o - 51^o. My concern is why is Big Mama having such a hard time with this when the others seem to be doing just fine. Appreciate any thoughts. Thanks.