Least effective class on PC?

They just need to learn to shut off cloak when going in for a kill from behind. This isn't possible in every situation, but in situations where it isn't one probably shouldn't be going for the PK anyway.

That's true enough, but that in and of itself makes the job harder to get done given that bot waves will probably shoot her in the back or some other player may well do the same.

Which is why you shouldn't go for the kill at all... If your back is so exposed when trying to backstab somebody, pick an easier target and stop being frag hungry. Assassins need Patience to be effective, or else they'll go attempting to face stab people which often fails. If you're in doubt you can get a kill and survive it's better to leave it and strike at a better time.