Hammer to the head

Not very likely. Sounds like way dead to me. Probably a basal skull fracture and major bleeding into the brain cavity, either of which is likely to be fatal. A standard claw hammer would be plenty effective for this purpose.

You might have to be more precise about "substantial force", but any average-strength adult could wield a hammer with enough to get the job done, if they were trying to kill somebody. It would certainly disable the victim, after which a few extra shots would remove all doubt.

And it would work equally well near the left ear.

caw

To both questions, possibly. You're the writer. You get to control how debilitated she is at the moment of this confrontation. Either you want her to escape, in which case she's capable, or you want her not to escape, in which case she isn't. I don't see any obvious physical limitation in play here, other than what you create. Getting hit in the head by a hammer, even weakly wielded, wouldn't be much fun for the receptee.

caw

If she gets an adrenaline rush, she can call on amazing reserves of strength. So in the heat of the moment would be better than going into it cold.

People have died from a single blow just with a fist, so dying from a hammer strike is perfectly plausible.

As the bird wrote, you are the writer, so whatever you want to happen will happen. In the real world the results from a blow to the head with a hammer would vary greatly, depending on who swung the hammer, and whose head t was, and it also depends on the hammer. Your hammerer was a weak woman who had been held in confinement, so she may have been weaker than usual.It wouldn't be surprising if the recipient of the blow survived but lost consciousness. If you want it to be a killing blow, then have her use a three pound sledge that she swings over her head and then down on the seated victim. For less damage she could use a light carpenter's hammer and be sitting behind the person and swing it up at the area you want hit. That would result in less force.

True story about someone trying to hijack/crash a cargo jet by attacking the pilots with a hammer (among other things):

http://en.wikipedia.org/wiki/Federal_Express_Flight_705

There's a book about the incident that details more about what happened and the injuries.

I would just add one thing.

The brainstem, underneath and toward the back is the part the controls vital functions like breathing etc., and the cerebellum (lower back part) controls movement. So IMHO, all other things being equal, a blow to the bottom back of the head, pointed up into the skull would do the most damage.

The thickness of the skull varies from person to person and if the person being hit with the hammer has a thin skull a blow could be fatal.

Yes, the variation in skull thickness is amazing. There was a skull in our lab in college that had to be half an inch thick. Solid, no sinus cavities. The guy in college headbutt anyone or anything.

Variation aside, the occipital bone, the one where the spinal column enters the base of the skull, has one of the thickest protuberances (thickened bumps of bone) in the entire body. This 'bump' is where the muscles on the back of the neck attach to the skull. When a body is cremated or eroded away by the elements and time, this is the portion of the skeleton that survives. This portion of the base of the skull might withstand incredible injury but, look at what's just below it: the fragile neck bones, spinal cord, and the base of the brain.

Of course we always expect the perfect blow or the worst case. Then, when we play the villian, it seems everyone has Achilles armor and a patched up heel. Each blow seems misplaced. We can't find our footing and our victim moves or wriggles or falls out of the way. Then, when we connect, the injury always seems worse than it really is. Our victim recovers unexpectedly.