Raz Taz...
I think leaving the food out all day for her is part of the problem. Lilly, our larger Golden Retriever, was gaining weight too. Our vet told me that as puppies, you should just keep food out all the time, but once she hit about a year old, he suggested feeding them one time a day. He said they will learn to eat it when it is there. I have two dogs, almost the same age, one that wasn't overweight. Lilly's weight gain stopped and she actually trimmed up a little. I make sure that when I do feed them in the mornings, it is a GREAT meal ! They actually stand there by the empty bowl, waiting for me to feed them. My vet assured me that they are getting enough. I do give them a Milk Bone in the evenings as a special treat. Sometimes they make that morning meal last all day as they know they aren't going to get anymore.
Hope this helps.