I bet it's driving you crazy! Maggie will sit and lick the air for a while but it's usually while she's spinning in circles on the floor. Bud will lick the air when we scratch his buttÂ

or clean his tail pocket. I always thought it was when something felt good to them or itched.
What is she on prednisone for? Was she itchy? I know you said she was doing this before the prednisone but if she was itchy before that she could have been licking because the itch was driving her nuts.
It doesn't sound like anything is wrong with her. Could you call your vet just to see if he's seen it before?