As far as assassins go, Ahri is one of the best buys honestly. With hard CC, super mobile, does partial true damage on her Q and can wave clear and deal massive group damage, there could certainly be worse picks. Even if you don't like assassins, playing her and getting used to an all-skillshot kit like hers can be useful for practicing skillshots with other champions.
She's also extremely forgiving as far as assassins go:
- Her ultimate lets her reposition herself quickly as well as provides a ton of chase and kite.
- Her Q's range is ridiculously long, coupled with the fact that it goes through minions, does a ton of damage and has a fairly wide hitbox makes it easy to land.
- If you get jumped on, you can drop your entire 100-0 combo while running away which makes her very lethal to try to chase if she has her cooldowns.
- She can dump almost all of her damage within the time frame of a level 1 Charm, meaning if she lands it on an engage, it almost always guarantees a kill.
- Her Ultimate+Charm combo is extremely difficult to dodge without a flash.
She doesn't snowball nearly as hard as someone like Katarina, Zed or Talon, but her utility, waveclear and teamfight presence more than makes up for any deficiency she has in raw damage. Plus, she's still an assassin. You get combo'ed on by an Ahri with any amount of a lead and it's very likely going to end in a grey screen for you.