BWI area isn't my expertise and we don't do Thai much and the Thai place we do go to is about 40 minutes from BWI.
Veg Baltimore looks to have some options:http://www.vegbaltimore.com/restaurants/
Most restaurants there should be within half an hour except Gaithersburg, Germantown (which kind of surprise me they are on VegBaltimore).
If you are staying overnight and want a nicer, dedicated vegan restaurant, Great Sage isn't too far of a trek. Google maps says it would take 25 minutes from BWI to Great Sage. There is also a nice grocery store next to Great Sage where you can get a variety of vegan junk food including some items from Sticky Fingers (DC vegan bakery). They used to have Cheezly but last time I went there, they didn't.