Brian,
I was bit pretty significantly by a dog in the summer of 2014. Rounded the bend to a viewpoint on a local trail here in Concord NH and had two Australian Cattle dogs (off leash) immediately run from their owner 200 feet away who was sitting having a snack break. One of them circled around me and big down on my calf and stayed clamped on with tearing motions for 15 whole seconds (which felt like a lot longer than that) and gave me a 6 inch long wound in the shape of the dogs jaw with a few deeper puncture wounds, one of which was near a major vein which a doctor said would have caused bleeding that would be difficult to stop in the field if it had hit it. Being a quick local hike I had nothing but a water bottle. The dog was a rescue dog. Owner was compliant on providing me rabies certification, but never even offered so much as to buy me new pants.
My oldest daughter was bit 3 times by dogs by the time she was five years old.
A few years later at the same place in Concord I had a woman's dog (off leash) charge and lunge at me aggressively (huge breed). This time I had my poles which I used to push the dog away. The dog was so out of control that the owner actually gave up on calling it back and she walked away from me down trail and left the dog with me, continuing attempted attacks. I couldn't believe it. I called out for her to get her dog back. She said she just got him as a rescue that week! She finally came back after I threatened to call the police.
There have been many other times on trail dogs have been aggressive to me. Last summer I had my five year old daughter climb Kearsarge (South) with me on her own power. She was proud and amazed at the summit views. 2 minutes later, an unleashed dog violently growling attacked a leashed dog, pinning the woman who owned the leased dog underneath. 40 feet away from where we were sitting. Scared my 5 year old and ruined her first big hike with daddy.
The sad thing is before the bite incident, I had no fear or ill will towards dogs (or dog owners). Now I honestly do. I have logged 6000 backcountry miles and have had 5 solo bear encounters and been followed by a pack of coyotes alone. Dogs bother me more than the aforementioned situations or anything else on trail.
And I don't feel safe bringing my now 6 year old, 3.5 year, or 10 month old daughters only popular trails anymore. I almost brought my daughter on the hike I got bit on--she was 3 and the thought of that dog biting her on the neck instead of my calf is a scary one.
This trend of irresponsible dog owners is increasing. Some of them seem to have no regard for other's safety including little children, the sanctity of a wilderness experience, or fear of being sued. I will sadly be avoiding 4k's this year because of this. It seems that the greater a locations draw on social media, particularly facebook, the great the number of inexperienced dog owner "hikers" who like posting selfies with their newly minted unleashed canine "hiker" pals on facebook. I have noticed a few people reporting being bit by dogs this winter on newenglandtrailconditions.com in the dog comments section.
But at least this woman in your story had a leash, muzzle, and she admitted he's not friendly. Usually all I hear is "he's friendly" as they barrel down on me growling.