If she's licking the air there may be something in her mouth which is bothering her and she is trying to get it out. Something stuck in her teeth, a sore? Check the inside of her mouth to see.

Some dogs will lick the air from teeth problems but air licking sometimes gets confused with something called flycatching. if the dog appears to be snapping at the air this is called fly catching and it requires seeing a neurologist. My best advice would be to try and get this behavior on video, it will help the Vets in diagnosing.

If she making a smacking, slurpy sound it's quite possible she's having indigestion. My dog does that (can be worse at night) and she has to take an anti-acid med to prevent it.

BTW..........there are much better diets she could be on than Science Diet, especially if she's have digestive problems.