I disagree with Killua's lightning negating durability; it doesn't do significant lasting damage, though I agree that it causes paralysis and pain. Rammot was able to tank Killua's lightning early on, but it still caused Rammot pain.
Demon Slayer characters have history dodging lightning, and Shinobu is particularly fast among the Pillars so should be able to close in even if Killua decides to use lightning.
Whirlwind and Speed of Lightning gives Killua a really good advantage, but he is unlikely to use them at the beginning of the fight. Killua can't use his electric abilities for long, and he needs to manually recharge afterwards by absorbing real electricity (such as from the wires of an electrical sockets), and since he runs out before he realizes it seems that he can't tell exactly how long he can use his abilities. So Whirlwind would be his trump card rather than something he opens with.
Shinobu has a sizable AP advantage: +70.1 Tons vs +22.13 Tons.
So she can overwhelm Killua's defense early on and score critical stabs.
Shinobu's pain tolerance is nothing to sneeze at.
Don't think poison will play a big role due to Killua's resistance.
There isn't a statement that Shinobu's poison carries doesn't affect normal humans, but I'd say it is likely some do. She uses different wisteria-based poison compounds for each demon so it affects them even if they adapt to an other wisteria-based poison, and her sheath is capable of switching between various poisons; information about poison used against demons is telepathically shared and they adapt in advance.
She uses extremely potent poison compounds not just typical wisteria; for example anti-demon paralysis poison that affects a normal demon for half a day can be shrugged off by Upper Moon 6 within moments.
