I often make treats. There is a little plastic container at Petsmart that has tiny, training treats. I forget what they're called, but they are definitely tiny, like a pea. I often do what Lizzybeth says; mozzarella cheese, sometimes cheddar if that's all I have (it's a little harder on their tummys I think than the white cheese, but that depends on the dog) left over chicken, pork, beef, salmon from last night's dinner. (it doesn't take much) Or for some dogs who are pigs, like Jose`, even kibble is considered good enough. (Some dogs aren't thrilled over kibble) As far as adequate reinforcers, just make sure she is crazy for the treat. Homemade treats are cheap and easy. Here's just one recipe I use. Some recipes that I've seen online have a ton of garlic in them. Be careful. Small amounts of garlic are good for them. Too much can be toxic.
1 container (not sure of the weight, maybe about a lb.) of chicken livers
1 egg
(puree in blender)
Mix in bowl with 2 cups of oat flour. (or any flour if you don't have oat flour)
1-2 cloves minced garlic
Sprinkle in a few pinches of parmessan cheese (to make it nice and smelly)
Mix well and pour into greased 8x8 Pyrex casserole baking dish (or metal)
Bake at 350 degrees F. for about 1/2 hour or until edges come away from the sides and toothpick comes out clean.
Take out of pan, cut into tiny 1/4 " pieces. (or as small as you can)
Let cool.
You can divide into baggies and freeze. I don't make the portions more than I can use in 2-3 days.
Let the dog lick the bowl. LOL.
Another fun thing that gives exercise besides fetch, might be hide and seek where you hide and when she finds you, give her a treat and praise. This can help with "come." Throw in your cue just as she arrives. Walks are good. You can be working on good manners as you go. It sounds like what you're doing is great. She probably doesn't need inordinant amounts of exercise. Like it was mentioned, excessive exercise might damage her bones and joints at her age. Later, you might enjoy one of the many dog sports that they have now, like agility or fly ball. You could even start her in a puppy agility class where she is introduced to those obstacles, but the jumps are very low, everything is low at first, the weave poles, she can do, but should go slowly through them. She can get started though, learning how to go through these things. I did that with my Doberman. It was embarrassing. Here was this big, tall 6 month old puppy jumping over jumps my Chihuahua could jump over. (at home, there was no stopping him. He'd jump over huge logs and jump off my porch which is about 4 steps off the ground) Those things were technically not a good idea, but like I said, there was no stopping him. LOL. At any rate, nothing happened to his bones or joints.