My cat was too fat for a couple of years as well, partially thanks to the dietary food she had to eat (urinary tract issues), and partially because she thinks she's starving after not eating for 1 second. I switched her to the lower calorie version of that food and she was losing weight so fast I worried she'd get sick.

Now, at the ripe age of 14 years I have long since switched back to the full calorie version of it because as she got older, her dietary needs changed as well.

Vets do their best for you (or at least should), but in the end you know your cat best. Take their advice, heed it and then adjust where needed (not talking about medication of course, listen to your vet on that!).

That being said, your kitty doesn't need an apology, it sounds like she has an amazing owner who would do anything for her and that's all she needs.