Not at all.
Ahri is pretty much my only mid laner (or at least my go-to) so here are my answers to the title's questions:
Weaknesses: Mana costs early, skill shot reliant for any poke, charm is very hard to land for how strong the cc is, her all-in is lacking if she's not fed (she can't 100-0 you even with ignite if she hasn't poked you down first), very squishy and susceptible to early ganks if you know which side she has warded.
How to play against here: Mana costs only allow her to use 1 Q per wave. Dodge it and she has no kill potential on you ever (if she uses more, engage when she's low mana). I normally find it worse when my opponent pushes against me to my tower (as again, I can't push back with Q unless I let myself go OOM). That said, if you have no push potential then just farm from behind minions and her Q poke will automatically push the wave to you (you should still dodge Q), letting you call for a jungle gank (which will likely work if she doesn't have ult and you tell your jungler which side is warded).
Who to pick: Ahri's worst matchups by a mile are Diana and Malzahar. She can't do anything to either of them, and they can both kill her at will. After those two, Annie is a great pick too. Syndra and LeBlanc were previously good picks but I haven't played those matchups in ages. I find Yasuo annoying as in the matchup literally everything is in his favor, but he's not a great choice of champion in general to learn, especially if you're only doing it to face Ahri.
Who NOT to pick: As an Ahri, these are my favourite matchups: Twisted Fate, Orianna, Vel'Koz, Xerath. I typically get fed in these games. Take Orianna for example, her only real strength is landing her ultimate. I can easily dash out of it, and doing so I instantly win the skirmish. On top of that, any jungler with reliable CC (e.g. Jax or Udyr) can get theirs on your immobile mage and I can easily follow up with charm for free kills in the early game. I beat you in lane, I out-roam you (except TF, but I can follow pretty quickly with MS quints), and I'm almost as strong in teamfights (stronger once you feed me).
Other 'tips':
Her "auto-lock ins" can hit minions. Make them do so (engage with allied minions present).
Harass is worth more than you think, her heal isn't up all that often and when it is she really wants to hit 5+ minions. If you can track when it's up, try to deny her the option (e.g. engage and force her to burn spells and thus the heal on fewer targets hit). I don't think many Ahris explicitly track their passive to maximize its healing potential unless they really need health though, so she's probably not using too much sustain anyways.
She's a lot easier to gank than she appears, as long as you know your path isn't warded.
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