I'm sure someone's already pointed out Meiling's character profile.
A "Chinese-looking youkai." Sure, one could say she's still a dragon, but the fact that the adjective "Chinese-looking" is there implies that is best (or at least a very good) description, leaving little room for any addition.
"By no means a special character." You could say it only means she's not special within the EoSD plot, but I think that's stretching things a little.
Building off that, you could also argue ZUN never explicitly states she's not a dragon.
But this is about as explicit as it will ever get, unless he says something in an interview. If Meiling isn't a dragon, do you really think he would go out of his way to say "she's not a dragon" in a profile?
Personally, I don't think ZUN's "silence" has much value.
Look at some various character profiles. ZUN lists hobbies, personality, relationships, backstories, and roles with surprisingly great detail. ZUN shouldn't keep something like dragon-Meiling to himself. Saying that makes him out to be some guy who tries to be sneaky and clever with his fans. If he wants us to know, he'd tell us. If he hides it, that's... Probably because it was never true.
And if you insist the evidence still leaves some room for the dragon-Meiling theory... You're right. But for me, the possibility is, at least currently, just too low.
Hoping these arguments haven't already been pointed out countless times.