Just posted her info on all three sites listed above.
I have new info from my parents about when/how they think she got out.
Apparently, she was last seen lying in the yard shortly before 7:30 PM on the north side of my house. My dad and brother had been doing yard work with the dog out back and were finishing up because it was getting dark. Boo didn't want to come in with my dad (I asked him if she looked like she was just basking in the sun or injured/ill in some way... he said he didn't notice anything awry). This is not terribly typical, but not unheard of either... she's not the world's most obedient dog and has been known to want to stay out occasionally. Anyway, fast forward and the neighbor to the southeast of us started setting off fireworks. My dad went outside to check on Boo. She wasn't there. He assumed my mom had already brought her in. And that is how she disappeared. So, provided that the fireworks did scare her, I suspect that she bolted in the Northwest, away from the noise.
I will upload a map later, but this would put her headed away from Davis Drive (in Lorton) towards furnace and Lorton roads (and eventually in the direction of I-95).
How far does a scared dog typically bolt? Keep in mind that the fireworks continued to go off even after she started running.
I am absolutely terrified that she made it to 95 without turning somewhere.