
Hi - your vet is right - a slim dog is much healthir than a tubby one. Do the stroke test - when you stroke your hands along her sides what do you feel? Bony ribs sticking out? Bumpy ribs beneath some covering? Or do you need to press hard to feel the ribs? If it's the second, then she's perfect.
Just like people, most dogs nowadays are too fat, and you start thinking that's normal ...
:)