The only birth control that I have heard of that encourages a lot of gaining is depo provera (the shot). Use literally anything else. Other than that, encourage her to use My Fitness Pal or another similar calorie tracking program, and perhaps a TDEE spreadsheet. CICO doesn't stop applying just because you have more cravings. It is not uncommon for birth control to change fat distribution, but it shouldn't turn a human into a ham.