I also encourage her to move around a lot during the day as best as a toddler her age can and will be enrolling her to play a sport/dancing etc when she's old enough as well as swimming early next year some time as that's a skill she definitely needs. We'll practice in my older sisters pool until then
There's also a psychological/physiological component that goes with obesity which has to be addressed once you're at that stage (and I've been there) as you have to understand your relationship with food and why you [insert whatever issue you have.... for eg....too big a portion size, emotional eating, sugar/junk food addict etc, etc] do these things as if you don't resolve it, you'll just end up doing it all over again!!
In summary...that's why it's not as easy as "less food in, more energy out" for the majority of obese people even though it's a common sense formula for losing weight and maintaining. It's all the underlying sh!t that's in control of the person mentally/emotionally.