my neighbor is claiming to be "dangerously allergic" to my 6 lb. well groomed Maltese. Yet, she does not claim to have any problems with any of the other dogs in the building. is it possible to be allergic to only my dog?

Actually, according to my Allergist, yes you can be allergic to a specific dog. Depends on your body's immunities and what is in that dog's saliva and dander.

It's possible to be allergic to one specific dog if there's something about its grooming that irritates you. But it sounds from your post that she's looking for a reason to have a problem with your dog. You're in an apartment building? Any chance she wants to make you get rid of your dog? Maybe she thinks your dog is an annoying yipper but doesn't want to say anything. So she pulled out this excuse instead.