I can not say how much diet has played a role in what is going on with your tort. But I am sure I would discontinue the frozen veggie regiment. At the very least I would switch over to fresh greens such as collard, mustard, etc. I would even go as far as to buy grass online or even use the dormant grass in your area to mix with the fresh greens. I live in Dallas and I use the dormant grass from my backyard during the winter months. In addition I would also start using a calcium supplement and UV lighting if you are not already.
my two cents
Allen