Sounds like the vet is a very nice guy. He's a keeper!
On the feeding, there are different opinions. The nuitrition section on this site, however, is an excellent conservative source. You can't go wrong with it. Things like fresh fish are great - not as a staple but as an occasional treat. Many people on here put live minnows or guppies in the tank for their turtles - can't get fresher than that! It also gives the turtles some hunting experience. The dog food, I'd avoid altogether, though, as it will be very high in protein and fat.
What turtles need and like that the vet didn't mention is lots of fresh vegetables. especially water plants like anacharis are good. It's normally a big part of their diet in the wild.
Also, it's essential that the turtle get plenty of calcium. Most people provide cuttlebones (the same kind that birds use) which is an excellent and inexpensive source. Chomping on the hard cuttlebone also keeps the turtle's beak from getting long and ragged.
Here's a link to the nuitrition section on this site. If you haven't read it yet, I highly recommend it:
http://www.redearslider.com/index_nutrition.html