That sounds like a load of rubbish to me. What kind of snake is it, do you know? If it's a smaller snake, it will know that she would be far too large for it to eat, and if it is a large snake she really shouldn't be sleeping with it anyway as it is a bit dangerous. Only the really big snakes would be able to eat a person so I wouldn't worry.
Also, snakes don't have the capacity to think "I'll not eat for a while then I can have a really big dinner". If something comes along and they haven't just eaten, they'll eat. If they have a big meal, they might not eat again for 6 months.