What should they have done?

-Kept an Eye on Her Weight.  Just because you're pregnant, it doesn't mean that you can throw away the scales!  Energy needs for expectant mothers only increase from 2000 cal/day to 2200, then 2500 in the later stages.  Weigh yourself regularly - if you were underweight before you became pregnant, you should aim to put on 12.5 - 18kg (2 - 3 stones), if you were of average weight 11.5 - 16kg (1 stone 8 - 2 stone 5) and if you were already overweight, you shouldn't put on more than 6 - 10kg (below 1 stone 5).  
-Eaten Healthily.  Think of both yourself and your baby and avoid sugar and fat, replacing them with foods which will help fetal development: proteins (meat, fish, eggs) for growth; slow carbohydrates (pulses, potatoes, bread) for energy; fatty acids (vegetable oils and butter) for the nervous system; calcium (dairy products) for bones and vitamins and fibre (fruit and vegetables) for general health and wellbeing.   
-Carried on with Exercise.  Keep moving, but leave out risky and high-impact sports like horse-riding, martial arts, the gym and jogging. Instead, go for more gentle options like swimming, aquagym, light gym classes and walking.