"Vintage Coward is the best example of Coward." (deadrat)
"Vintage Coward is better understood as a somewhat more literal use of the metaphor: "characteristic of Coward's best period". (StoneyB)
I'm with StoneyB. Here are two definitions I found at http://www.thefreedictionary.com/vintage to back up this point of view:
Serving to identify or set apart an individual or group: characteristic, distinctive, individual, peculiar, typical.
representative of the best and most typical: vintage Shakespeare.
Now back to your original question:
The reply was vintage Emily.
In practice in recent times, the meaning has been extended even a bit further than what StoneyB said. Here's an example: Suppose Andy, a mediator who's been trying to help you reach a settlement with a school district, is an eternal optimist, and you're discussing Andy's latest expression of optimism with B. Here's how the dialogue might go:
You: Did you see the email that came in from Andy this afternoon?
B: No, I was busy in the lab all day. What did he think of the district's latest counter-proposal?
You: Vintage Andy. You know, "Let's assume the district is negotiating in good faith, bla bla bla."
B: Yeah, I know what you mean.
"Vintage Andy" means that Andy was behaving true to character -- however that might be. It could be charming, it could be endearing, it could be maddening, it could be anything. This is like Definition 3 above, but maybe even goes a little farther.
I don't know exactly what Emily's creator had in mind, though, given the lack of context or link.