Don't make her wait too long at first. Let her succeed at sitting and waiting for just one second or 1/2 a second if need be...and then hurry and shove the treat in her mouth and immediately release her. (get a release word in there fast) You can choose whatever word you want, like, "okay" or "release" or "free" ...just use the same one. This release word is very important for waiting, sitting, lots of things. That tells the dog that, good, you sat, now you may get up.....so she doesn't break the stay or wait or sit....whatever. Again, don't make her wait to long at first. Build duration gradually in low distraction areas.
Now, once she is reinforced many times for waiting for one second and she gets the treat BEFORE she gets up, she will learn that sitting and waiting
WORKS to get the treat. But getting up or lunging does
not work. If she does break the wait or sit, you've waited too long and you can not let her have the treat. Swiftly pull your hand behind your back and wait and see if she'll sit on her own. Don't scold or even say anything. Try waiting. This will help develop the default behavior of sitting when you have a treat. If she still doesn't sit for quite some time, you can remind her again. Just try not to get in the habit of repeating cues over and over.
Once she gets onto waiting for one second, increase to two seconds, then three. Only increase the duration as she is successful with the previous duration. If she messes up, you're asking too much, too soon. Go back to where she was successful and work up again.
Make sure she's getting plenty of exercise and mental stimulation. (not sure what you're doing with her) This can help to settle her down. Work on obedience every day....a few very short sessions. Use positive reinforcement type methods so she'll love working with you.
Here are a few good links. Relying on this concept is a must with dog training:
26. Zen
One of my very favorites:
How to Train a "Crazy" Dog! | Karen Pryor Clickertraining