It's worth keeping in mind that a maternal BMI of 35+ will likely translate into transmissible problems far beyond obesity. The mechanisms will be patterns in upbringing related to responding to stresses, and by epigenetic processes just beginning to be uncovered.
An opening step in understanding the underpinnings of obesity will be to determine the age at which weight gain first began, then asking the individual why they think it began THEN and not three years earlier or ten years later. Sometimes a meaningful insight is delivered; the rest of the time a seed has been planted for later harvesting. The other big question is "What are the benefits of obesity?" because major weight loss typically poses an unrecognized threat to the person losing the weight. This latter question is most productively asked of a group of obese patients rather than with individuals because of the mutual support in such a group, given a threatening question.
In addition, we have found a questionnaire filled out at home, before coming in, to be very helpful. The one we developed over the years is attached. Feel free to take from it. Good luck in your work!