I agree with Karla. I would, however, try to do a real good inspection of her mouth, way in the back and around the gum lines. Roof of the mouth, etc, just in case she has something stuck. Not unusual for this to happen if they chew on sticks or plastic. Agree to have her checked soon as you don't want to have to deal with a bad infection. You feel any swollen nodes under the jaw?
Possibly an abscessed tooth.....You really don't give enough information, here, but that's the first thing that comes to mind.....
You need to have it checked by her Vet.....If this is a bad tooth, it can lead to many problems.....Left untreated, the infection can enter the bloodstream and cause heart problems......
The tooth will be extracted & antibiotics given for infection.....Also, chances are high that your dog will quit eating because of pain...This leads to other problems, too.....
Have her checked as soon as you can.......Karla