Our little terrier mix mutt has recently started behaving a bit strangely. Whenever strangers (to her) come to our home she barks very aggressively - almost to the point of scream/barking (never heard a dog do this except when injured but it's almost like a combo yelp/bark). She then proceeds to hide under a bed and continues barking as long as the stranger is in the house. My young nieces visited recently and she even went so far as to try to nip at one of the girls. 

Even with no strangers in the house, any slight noise inside or outside elicits a bark or a growl.

The only thing we can think of is that she recently had a pretty traumatic visit to the vet. She didn't respond too well to having her nails clipped (did the same yelp/bark/scream thing during the process and needed to be muzzled). We are wondering if she is suffering some sort of PTSD from the event. Our previously calm and sweet puppy is now a nervous wreck.

Would love any advice or ideas on what to do to help her come out of this!