How are her organ functions ? (kidneys, heart, liver etc) Is the vet sure this weight gain is caused by over-eating and not water-retention? (or ask your conscience...did you over-feed her before?)
An overweight dog who is used to not exercising may find itself lethargic when suddenly asked to get up and walk or play. But if she has been playful, and ready for a walk before, and this lethargy has happened suddenly, then it points to her feeling unwell in some way.
Purina foods are NOT the best choice, even if recommended by a vet. Their study of animal nutrition is extremely limited, when they are at veterinary school. Not many vets have a proper grasp of it, surprisingly.
There is nothing wrong with a home-cooked diet, but it would have to be researched properly.
Do you know what thyroid tests were run and what the actual results were?
You've gotten some good feedback, above. I'm with Misfits4me in thinking it might be helpful to have a little more specific data -- like what were you feeding when she got overweight and how much, and what does she weigh now. I would add to that, what is the goal weight for her, just so we know how much she needs to lose?
I can tell you that, with one of my dogs that tends to overeat and be overweight, I have not found the weight control-type of dog foods to be helpful. Those have a lot of bulk added, to reduce caloric density. They tend to be low in both protein and fat. In other words, they don't have a lot of nutrition in them. Most of the calories that they do have in them come from carbs. From studies of human weight loss, we know that a high-carb diet makes you hungry, and that seemed to be the case for my overweight dog.
My chunky dog is much happier with a high-protein food. She was constantly hungry on the "diet" dog food. I ended up putting her on kibble that is 30% protein and 12% fat. In other words, the protein was high, and the fat was relatively low, but those still weren't the most extreme proportions you can buy. (CORE Wellness Low-Fat kibble is 33/10.) My dog seemed happy on that and did lose the extra weight. I strictly controlled portions, or I'm pretty sure she would not have lost weight.
The whole process of weight loss took a good six or eigth months, because I wanted to go slow and not stress the dog. She was about 15% overweight at the start, and now she is down to an appropriate weight for her. Now that she is on weight maintenance, rather than weight loss, I am less strict about the percentage of protein and fat than I used to be, but I plan to stay between 28 and 30% protein and 12 to 14% fat for the forseeable future.
For my dog, the two keys were controlling portions and using a dog food that didn't leave her feeling hungry. If you are controlling portions for your cattle dog, and if she is getting no more calories than she should, and her thyroid is normal, I really don't have any explanation for why she isn't losing weight.
Welcome...What food were you feeding and how much? What does she weigh?
I am sure there are many advocates on home cooking for dogs, but I think I'd try some dog kibble that is grain free, and limited ingredients... said another way not one of the many popular brands that are full of junk, floor weepings and fillers. I guess the "good" thing about some of the fillers is they don't contribute much to weight gain.
Be sure she isn't getting table scraps, lots of treats or other inputs to her diet. It sounds like exercise is already on the agenda, keep it up... but in the Colorado high lands (what is Sterling about 7,000 feet?) all need to adjust to the lower pressure/oxygen. You said one year old, how long in your family?
I'll have to look up Old Blue Heeler, sounds interesting. How much should she weight? At 1.5 cups in most kibble I'd guess 25-30 pounds is the objective. Keep in mind too, a young dog needs some a higher energy/growth food.. guess 1 year if full grown, so that time may have mostly passed.
All us with a weight problem have to work together - keep us posted, both my Westie and I could stand to lose about 10% of our current weight. My Westie eats a Nature Balance Sweet Potato and Fish grain free, Westies are susceptible to food alergies.
Purina is not the best food. Try buying a new food for weight control with lower fat and protein.
At least thyroid was checked and ruled out.
If you want to fix your own, balanced diet at home, do some searches on the Internet for recipies.
. You can also look up the BARF diet, which many people feed.
I seldom had overweight dogs but for those packing on a few extra pounds, I used the green bean diet. You cut each meal with half their regular food and half green beans. I used canned and rinsed before adding.
Of course. Exercise or a couple of good walks a day help.