People fight for custody of animals more than you'd think during a divorce. lol Any who!
So for me, it seems like food isn't the only issue. There is a loss of weight, change in behavior or attitude of the snake and lack of a heating element. All of the above equals stressed out snake!
If she "needs" you to purchase the feeders for the snake but retains possession of the animal (stated in the divorce decree or not.) She could just pay you back in cash but you run the risk of being screwed over. Where you pay to maintain the snake but she retains full possession.
At the end of the day, If you feel she is not adequately taking care of the snake you need to talk to her and try to get him.
If this was me, I'd take him!!!