E does double damage if they are 'chilled' from one of her other abilities. Once the cold effect wears off they take normal damage from it (which isn't much).
Reds combo's typically start with an amazing wall and he has good knowledge of game mechanics.
Someone will be running away and he will drop a wall in front of them which usually connects on one side to impassable terrain. This will cause their champion to take the path of least resistance, which you can actually predict even if you don't connect the ice wall to a real wall. And so as soon as the wall is down he has an iceball going in the direction that they are now forced to take, the direction that their champion will automatically be moving even if they don't press anything. And so unless they have crazy good reflexes to change their new pathing they are ice balled and E'd. And even if they dodge the iceball they are usually dodging into the meat of a well placed Glacial Storm.
The thing about well placed walls is that even if they (your opponents) are playing perfectly they are usually forced into a disadvantageous situation. Either that or the expend a flash to get over the obstacle, which is still a win for your side.
It's one thing to know the abilities and generally how they should be used. It is quite another thing to have actual mastery of your character and be able to make execute the abilities with split second decisions. Red can do this with Anivia.
(And as his primary partner I know what red will be doing upwards of 95% of the time as he's doing it so my own decisions can further punish them for reds pro play, but that's just good teamwork)
Also people will tend to back off when the R drops to avoid a frostbite, but what you can do is toss the frostbite first and use super speed to drop the R around them (and get the chill effect) while the frostbite is mid-air. It can be a good way to get some unanticipated damage, but usually the theatrics are not necessary.
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Eff_Dee