If I recall correctly, older models of Nekovalkyrja had slightly more robust skeletons, including bone plates under their forearms to serve as makeshift last-ditch bracers. They were nearly immune to most poisons and drugs, though, they could selectively allow certain chemicals to take hold while their immune systems shunted anything unwanted to their claws - the notable exception there being Mishhu venom, which seemed to be tailored specifically to break through this protection. Diseases were not a concern in the slightest.
As for their ability to endure straight physical damage, that seemed to be an all-or-nothing affair. If you were shooting or stabbing her, then you probably hit a thrice-redundant organ and she would regenerate nigh-instantly and kill you - or you tapped her brain and she fell like a sack of potatoes. Other common methods of killing them were blowing them to bits, incinerating them - they cannot regenerate over cauterised tissue - or irradiating them. NH-17s and previous were also largely biological but genetically engineered, and the content-protection built into them would detect attempts at genetic scanning, throw the neko into a few seconds of berserk rage in hopes that the source would be destroyed, and failing that, she would self-destruct.
The most reliable way of bringing a neko down was to wear her out. The largest combat advantage of the NH-29 is that she only eats as much as a human. The more military nekos could fly, walk on ferrous walls and ceilings, turn invisible, regenerate, project tentacles, and hurl steamrollers, but all of that is very draining. It generally took no more than five to fifteen minutes of constant exertion for a neko to simply pass out, unless she could somehow stuff food in her mouth constantly.
