I would not order from Chantel's. A member of a local allergy support group ordered from there several years ago, and what they ordered ended up having the allergen in it. They make items with nuts, dairy, and egg. I just would not trust the risk of cross-contamination in such a bakery situation.
We routinely buy chocolate from Simply Nut Free. They are at our local farmer's market (Brambleton) most Sundays (until it gets too hot). She wasn't at Brambleton last week because it's gotten too hot. I know the owner. The chocolates are great. She also makes a yummy pretzel bark and soft caramels. It's definitely worth ordering online.
There's also a Clyde's in Tyson's. We have also eaten safely at BGR at Tyson's Corner Mall. DD just gets her burger without a bun if she gets a full-size burger. If she orders sliders, she gets the bun; it's a Martin's potato roll bun for the sliders.
If you're in Brambleton, the Blue Ridge Grill is good and has been fine for DD's allergies. The owners used to work in the Great American chain (as did the owners of Ford's Fish Shack).
BTW, Brambleton isn't 30 minutes from Tysons. As if you couldn't tell, I live in Brambleton.