I want to help my excitable/ anxious dog learn to settle, but high-value treats (and even attention) are exciting so we end up in a heightened state. Even if I try to capture a moment of chill, once I give the treat she is amped up. How can I help teach her to relax or reward relaxed behavior?

Try the following;

Teach a “calm” behavior – remember “slow is fast, fast is slow”.
Make sure your own energy is calm.
Prepare the environment for CALM such as a quiet home.
Put a lower value treat in your pocket (leave the training treat pouch out of this training session).
Instead of a clicker you can use a verbal cue such as “yes” or “good” in a calm tone.
If you prefer to use a clicker, try a clicker that is quiet or put the clicker in your pocket to muffle the sound.
Once your home is quiet and you are calm, sit on the floor with your dog on leash and wait.
Be sure not to give your dog attention (especially for unwanted behaviors such as high energy).
If your dog does a calm behavior such as sitting or laying down give them a treat and calmly say “yes” or “good”.
Try to avoid eye contact (you can add this into your plan later).
After about 3 to 8 minutes of training end on a calm note.
Practice this each day for a short period of time. Remember, consistency is key!