mangeorge, the resolution of the case in a court of law would depend upon the jurisdiction.
We start with the basic concept of negligence. Did the defendant owe a duty of care to the plaintiff, did the defendant breach that duty, and did the plaintiff suffer damages as the proximate cause of the breach?
Well, yes, the defendant owes a duty of care to the plaintiff. The dog is known to be aggressive; a reasonable person would assume this could lead to a biting attack. Indeed, the defendant clearly understood this as demonstrated by prior behavior. The defendant is inviting the plaintiff onto her property, thus the defendant needs to take reasonable steps to ensure that the plaintiff isn’t bitten by the dog. The plaintiff didn’t arrive at a totally unreasonable time, so the defendant won’t be able to say that the duty to protect the plaintiff hadn’t started yet. (I should point out that one could analyze this without the need to be specific to this case of an invited guest; the property owner has a duty of care to anyone who can be reasonably expected to come to the door).
Did the duty get breached by leaving the dog on the porch tied up at 3:30? This gets trickier, but a trier of fact could reasonably decide yes to this question. After all, as noted, the plaintiff’s arrival a bit early perhaps should have been anticipated. Further, leaving a dog that might bite someone on the porch tied up without supervision in reach of the path to the door isn’t exactly the most reasonable approach to things. Yes, an argument could be made that the duty of care didn’t really kick in until the defendant could reasonably expect the plaintiff to arrive, and that point hadn’t been reached, but it’s not impossible to come to the contrary conclusion.
In this case, proximate cause and damages are not debatable, really. Thus, negligence lies as a valid cause of action.
Now, you have made valid points about the concurrently stupid behavior on the part of the plaintiff (oh, the aggressive dog is out on the front porch; what the hell, I’ll just go up anyway and… OUCH!!). The trouble is this is where we have to look at the applicable law for the jurisdiction in which this happened. In some states, old contributory negligence laws apply. This means that, unless the plaintiff was MORE at fault than the defendant, the defendant is liable, and liable for the whole amount of the damages. In other states (e.g.: California), the defendant is only liable for the %age of their own comparative fault; thus, if the plaintiff was 40% at fault, the defendant only pays 60% of the damages. In still other states, some hybrid form of these concepts applies.
Mind you, this is a VERY sketchy answer to what could easily be the start of a good law school Torts class exam question on negligence. There are some interesting nuances I’ve skipped over. Still, the point is that Judge Judy might have been completely correct in her result from a legal standpoint, and from the standpoint of what a reasonable trier of fact would have concluded. Or, she might have had her head up her ass, where it usually resides.