That's my guess as to the main reason he picked it. But weight loss is also a side effect of Wellbutrin, though it's not very significant. It's a mild, mild stimulant so there is a little energy boost there which could help with exercise and also the motivation to exercise and be more active. In the beginning, the stimulant effects are more pronounced- it's possible the doctor was also thinking that she'd get a psychological boost ala "this is the drug that will finally help me lose weight" and it gets her into a healthy cycle of eating and curbing her appetite, while giving her the energy to exercise- even though those effects wane over time in most people, at least it would get her into a good cycle upfront.

-yawkaw