Her Q gives her free mobility for no reason at all, her ult makes her ungankable, her e not only disables you but SLOWS you. There is no WINNING against ahri in lane, there is only NOT LOSING. What the hell remove some of her mobility, overloaded as hell for no reason.
Actually, if you want to beat an Ahri mid, just bring in Sona.
Sona is an incredibly cheap early game lane-bully that pretty much becomes an AP assassin mid game and a supporty mage at late game. And when i say cheap, it's because you can dodge pretty much any skillshots if you put any effort to it, but no one can dodge your Q and AA combo. It's guaranteed damage that an Ahri can't really heal, and if you're good enough at avoiding skillshots so you only use heal minimally, she will deplete her mana pool much earlier than you will. Run her out of mana, then kill her. When i have extra money i can't use for building my items i usually grab some Faerie Charms along for the buffed up mana regen, it really helps Sona stay ahead.
What you have to watch out for; CSing. You have to CS very well or most Midlaners will outfarm you and outscale you in mid-game. Try to do your combo Q+AA on Ahri while next to a minion your second Q shot will kill, and don't hesitate to use your Q enhanced AA (not necessarily counting powerchord) to CS more easily. Then, who can gank you? If no hard engage-go full AP and wreck things up. If the enemy team has a J4, Lee or Vi jungle for instance, you'll want to build health during mid game (basically right after rushing the Sheen upgrade), i suggest Rod of Ages as it also enhances your mana pool.
I normally use something similar to these builds;
or
Yes, i'm a terrible human being and Runeglaive Sona is a thing. I actually just smacked a fabled Runeglaive Ezreal's ass while playing it.
I honestly liked laning against her more when she had the amplification on her E but no MS boost on her Q. As it stands, it's nearly impossible to catch her or get away from her.
A Talon main losing to Ahri. LOL!
stfu, learn to counter and git gud. i've never had a problem.
here now stfu 
when I'm playing lee sin mid, insanely infuriating
when I'm playing an actual mid, i really couldn't care less until it gets to teamfight stage where her charm just hits SOMEBODY every time
You know, when someone has the second lowest movespeed tier, I'm inclined to think they deserve a speed boost.
You can outplay most of her damage (Q, E; you'll only ever really get hit by W if you're in really close range).
If you have trouble dodging her Q, note that most Ahri players try to hit you with a max range Q so true damage is always taken. If this is the case simply moving vertically instead of horizontally is better.
As for her mobility: Q is a good movement speed buff but it's nothing like a Kat E where you can use it to blink through walls. Her other form of mobility is tied to her Ult, which I think is a fair trade-off. Either you use it to get away form situations, losing damage, or you use it to finish someone off, the latter leaving you vulnerable.
