The thing is, if 3F+K whiffs, nothing happens. If 66K whiffs, you're kind of screwed. 3F+K also has a better hitbox and is also a mid kick. And it's 0 instead of +1 on block, not a big difference there. If 66K gets hit on on counter, it's HCH. 3F+K is not as easy to crush as 66K. 3F+K is a sitdown stun on normal/CH, 66KK4 isn't that deep a stun in the first place. So technically as a ranged poke, 3F+K would be superior in almost every way. And you're not taking into account any other mid range options she has such as BT 6P, 3P, BT 2K, BT 2P, etc.. She has solid options at mid range to prevent being predictable, no need to do things like random 66K and drill kick.