I agree with Mika. She looks like a pretty good weight right now, judging from the pic you provided, Also she looks like a real sweetie.
In terms of food and amounts. I do the "feel" test, at least once and sometimes more often per week. That is I feel their ribs and spine, and also view them from above.
Ribs should be covered with a thinnish amount of muscle/skin, the spin should also not be sharp under your fingers and too easily palpated. When viewed from above, there should be a mild tuck up at the loin/groin area.
If you have a very active day, lots of walks n play, then I bump up the food by at least 1/4c cup.
Obedience training; good for you! I truly believe all dogs need it! BTW Yorkies do have a rather large guarding instinct. Barking at noises and intruders et al. Talk to your trainer about it; have them suggest some training techniques. There are more than a few approaches to this. Just be consistent with the one you choose. Apply it every day for at least one month, then if no success, it is time to try another method
