This is a situation that calls for a visit to your veterinarian asap because she's obviously in detress. It could be anything from an allergic reaction to a heart problem to an infection. Sometimes brachyocephalic (squashed nosed) breed dogs likes boxers, Boston terriers, pugs, bulldogs, etc, may periodically do some snorfling because the back floppy part of the roof of their mouths blocks their airway if they hold their heads a certain way, and that's another possibility.
Because there are multiple reasons why a dog would do this and some may be serious, it's better to have your dog examined to find out exactly what's going on.
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