Birthday catering in DC
Do you mean steamed blue crabs? That would be expensive and not worth the expense in a home-catering situation. They'd have to be made off-site and trust me, steamed crabs don't travel well.
Given that this is for your elderly mother in Georgetown, I'm guessing she's a traditionalist, and perhaps a long-time Washingtonian, so why not go with a traditional DC-area caterer like Ridgewell's?