(Sorry for putting this after many other ahri posts.) My idea to fix Ahri's charm.

Lower the duration every time they are damaged by a champion.

For example, at level 1, the charm lasts 1 second. Every time they are damaged by a champion, the duration should lower by 0.25 seconds.

It would increase with rank, obviously, meaning:

Charm: 1/1.25/1.5/1.75/2 seconds Reduction: 0.25/0.3/0.35/0.4/0.45 seconds

Now ahri cant use her entire EWQ combo on you and then have you still charmed in order for her to hit you with her ultimate, but she can still use it fully for defensive purposes.