suggestion for additional lissandra passive

right so is in an interesting spot after aftershock was nerfed and I think riot could push her identity as a chaotic cc battle mage. Problem is her only real durability comes from a rune & her ult. I think they could bring her up to a suitable (but not overbearing) power level with either: a) slightly buffed base damage b) slightly buffed passive (e.g. increase thrall MS or somethin) or c) A new additional passive whereby she gains a stack every time she impairs a champion's movement. These stacks fall off after something like 6 seconds and grant 1 armor and 1 magic resist. Stacks could then be capped at a value dependent on level (e.g. 10 @ level 1 to 40 @ level 18)

Thoughts? Discuss