This is my own take on Ahri Support. It's a bit odd to make a guide for, and I know a lot of questions may come from it, but this build is based around your team being able to capitalize on your plays. You pretty much have the same sort of ability as Thresh here, where your charm is a death sentence. Again, you don't have to agree with it, and you can leave your questions and feedback below, and I will get back to it ASAP.

The pros and cons are quite obvious but I will list them.

Pros:
Charm is an extremely powerful engage
Font of Life paired with Charm and Augment work well together
It can fool the other team into attempted counter-pick in mid
Lots of mobility to support every lane
Can pair well with nearly any ADC (Best bet is Vayne or Jhin)

Cons:
She can't be used to her full potential
Very low damage output in this build, must rely on team
Healing from FoL is not very amazing unless you have keen communication and an aggro ADC
Very squishy, can be easily caught if out of position
Leaving lane to help another lane could cause your ADC to be killed due to poor rotation/comms.

Takeaway:
Be careful with your roaming, if mid-lane is struggling let enemy bot push to tower and go help out. Try your best to accompany your jungler and set up ganks for them. Ahri is very squishy with no heals or shields, so you have to be reliant on your font of life. Be sure to auto the enemy bot lane as much as possible while remaining safe, you can get Eye of the Watchers pre-10 if done correctly.