So how the fuck am I supposed to fight this

Blitzcrank grabbing her, Hextech deactivating the items, assassins jumping to her, sorcs exploding her, knights shrugging off the damage, Vi saying Hi, or your own hyper carry doing the same thing she's doing.

Failing that, you realize it's ok to not get first and accept that you got beat.

With a long stick

well jinx is broken, but draven with the same items or even ashe with glacials would also rip ur ass off.

The simplest way to counter Jinx is simply to know cell placement, and not put one of your first to die in a possible direct line of fire of her.

If her TEAMMATES (not her) kill a champ, she won't excite/rocket. Make her attack a heavily spammable Braum or something, while your team takes out her front line.

Be mindful of whether or not Crits/Magic damage are more of a risk to your team. build counters to those in your front line.

P.S. Jinx Rockets do Magic damage + her basic. In other words, Dragon's Tooth counters her damage per hit hard.