I am actually fully aware of what her kit does.
It's a pretty intricate dance she does with her opponents because her spells all require her to be a certain distance away.
Q needs you to be close, but you get the damage when you don't spam it.
W needs you to to be far away to get the sustain off, because she only gets the heal and increased damage off the outer edge of her cone. If you're close she gets nothing but lessened damage. Kinda like a conical version of Darius's Q.
Her E is completely useless without walls, but she can jump to walls to escape or engage with a dive. The dive stuns and gives her an attack speed boost for a short time.
Her R forces a fight basically.
So as Darius, you want to stay in her face so her W is useless and if you're fast you can scoop her out of her E with your own. When she hits you with her first Q you can back off so that her empowered one will miss.
Also, I wasn't aware she ran thunderlord's but then again I'm not all that surprised.
Also, you're just not familiar with all the quirks of her kit yet. When you do you'll realize she plays like a diver along the lines of J4 or Xin Zhao in that they force fights, and you know how well Darius fights divers in general.
Also, her only peel is E, which is delayed enough for it to not be able to save a carry, and her R does nothing to peel the guy you're ulting.
Just fyi.