How did the vet appointment come out?
Take her to the vet. A muscle cramp would only affect one muscle - they eye has at least 4 controlling it and the jaw muscles are completely seperate. What happened may be nothing but may also be a warning of an upcoming stroke.
If it is a small stroke (TIA) here is some info:
(from strokassociation.org - but also applies to pets)
Also called TIAs, transient ischemic attacks are minor or warning strokes. In a TIA, conditions indicative of an ischemic stroke are present and the typical stroke warning signs develop. However, the obstruction (blood clot) occurs for a short time and tends to resolve itself through normal mechanisms.
Even though the symptoms disappear after a short time, TIAs are strong indicators of a possible major stroke. Steps should be taken immediately to prevent a stroke.
Like I said, better safe than sorry and if it is nothing then you have an updated set of labs on your shitzu and wasted an hour but if it could save her life, it's worth it.
Let us know.
It sounds like a muscle spams but a quick call to the vet might ease your mind on it.