Why did one die and not the other?

About three months ago a friend gave my fiance and I two pet ball pythons. He told us that they had both recently eaten. The larger female (The owner of a pet store where I believe the snakes were purchased told us that he was fairly sure it was a female) was about a foot and a half long and a good eater (We would feed her two mice ever two weeks or so and it make her happy) but did not like being handled much. She was fine after you got her out of the cage but before she would not really like it. The smaller snake (Little less then a foot long) is still exceptionally people friendly to the point that he will even sleep with me if I am napping (He/She/It will wrap around my arm or snuggle under my chin and stay still), but has not eaten since we got him/her/it. Worried we took him to the pet store to see what tips the owner could give us. The owner prodded him a few times and pinched his skin on the fattest part of him and told us he was not dehydrated and was very active and alert so not to worry because fasting was common in snakes even if they were small. He also told us to keep trying so we stopped worrying. At one point we saw a mite in the cage again consulted the owner of the store and he told us how to clean the snakes and the cage. We did everything he told us and have not seen a mite since, this was about two and a half months ago. Since this happening the larger snake had eaten without any problem and appeared mobile and content. She had also shed a very healthy one piece skin. Which I was told was a sign of good/happy snake. However when my fiance and I returned the other night it was to find the larger snake on her back and smelling rather foul with the smaller snake appearing to cower in the corner away from her. (We had checked on them both the evening before and they had been fine, my fiance tells me she smelled so bad because we keep the cage at about 90) The smaller snake is still as people lovable and not eating but just as active as ever. My fiance tells me I'm buying more worry then I can afford but I am rather attached to the tiny guy and want to make sure he lives... A lot longer any one know what might have happened?