Since she sometimes finishes all the food in one sitting, can you only put about half her amount in the bowl and if she eats it all, the other half later in the day? Not necessarily a schedual, but just so you'll have something to give her later if she eats alot that day in the morning without giving extra. Free feeding is fine, but you still have to only offer the daily recommended amount per day (adjusting according to the dog of course).
If you put it all in the bowl that she should have that day, when she eats it all, that's it.
If she's gained weight, you do need to cut back - if it's only because you've been giving that "extra" on the days she eats it all early, just cutting that out should help her get back to a good weight.
If you want to give her veggies to help her feel more full, try cooking them gently. My dogs all love veggies, but the won't eat them raw, only when they're soft from some cooking. Steaming is best if you can
