I haven't found a single champion that does well against her. Anyone have any idea's? Is elise good? Or is she too, bad?

Would Kassadin work? I don't think he would because of his bad early game.

Cho'gath mid?

Have you tried Lee Sin. If you want a more traditional mid, try Gragas.

Morde bends her over and shows her who is #1

Swain also does really well from my experience.

Agreed, Morde beats most assassins at mid.

Rhyze..stuns the balls off of moon *****

Jayce. Shock blast into acceleration gate whenever she attempts to farm. Do it 2 times, then transform into MC Hammer form and finish her off.

Anyone who can strafe right

Yeah, there are two ways to beat Diana.

Morde EATS Diana. If she tries to harass him, he has the shield to block it. Furthermore, Diana has no sustain, so Morde can harass her with impunity (especially since she's melee). If Diana goes all-in melee with Morde, he can just W-Q-E-R her and be on his merry way.

Swain is also an excellent counter. He can harass her easily with his Q and E, he can sustain her pokes with R, and if she goes all-in, he can cast his Nevermove beneath him and walk away.

tanky mages Ryze and Swain do well. Dot's like cass also rip her shield off before it can reproc.

Cho'gath kicks her ass hard. You can out sustain her poke, and you're too tanky for her to burst. Just poke her down with auto attacks and your W, then go in for a kill with Q when she gets low.