This sounds like it might be either a possible allergic reaction to a insect sting or bite or it might be a puppy illness called juvenile cellulitis or puppy strangles (name is worse than the disease). Usually you see skin sores with that though.
If the pup has any cuts or bites this could also be due to infection.
Pitbulls as a breed are know for skin problems, allergies, and immune system issues.
You can read about puffy faces here
http://www.petplace.com/dogs/facial-swelling-in-dogs/page1.aspx
If your dog got any tylenol that might be the problem too.
You should have your vet check her out.
Hope this helps you!
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