Assassins are not MEANT to have hard CC. That's what assassins are all about- getting in, kill quickly and getting out with NO TOOLS meant to help them stay in a fight.
**Their whole class is meant to not have hard CC so remove it, Riot. A minor slow like Zed or something, sure, but NOT A STUN! **
This goes against the whole philosophy of what assassins are about, and whoever added this into her kit, needs to rethink about what they are doing before they add things in that are NOT MEANT to be there.