Then today, I found out more about her. Berdina is actually a pit bull, even cuter than I originally thought, and she's a foster from the Washington Animal Rescue League. She ran away on April 20th and has been spotted several times since then.
If you see her, contact WARL at 202-230-4493 or 202-375-7755.
I'm not sure how many people who read this live in the DC metro area, but if you do (or know someone who does), WARL set up a Website to help try to find her. It's located here. It looks like she's been seen around Chillum and Kirkwood Parks in Maryland.
I'm going to make some time this weekend to go out and try to track her down. Hopefully, someone will find her and bring her back and it won't be needed.