Quorra is a powerful support and a counter-carry. Now, I say "counter" as opposed to "anti" as Quorra lacks "the big finish", and can only really secure kills if her opponent tries really hard to die. This is why she is an ideal duo-lane champion, as she relies on a team mate. However, this doesn't mean she cannot solo lane. Impasse is a very strong defensive skill, immunizing her entirely from damage and negative effects. Cast Impasse on LeBlanc as she goes to insta-kill you, and LeBlanc will find herself now on cooldown and Quorra completely unscathed (except perhaps the initial Q).
A typically support tactic would be for Quorra to cast Impasse on their carry, preventing them from focussing Quorra. A good support, after all, needs an anti-taunt to prevent them from being focused (the opposite of a tank, who wants to be focused). Then shield her ally with Revitalize when they start taking damage. This is why I mentioned that Revitalize must be considered sourced from the target; if Revitalize was considered to be sourced from you, it would not slow the target of Impasse (Quorra still gets an assist due to shielding her ally). Revitalize is very strong against champions, to help them chase or to prevent them chasing.
Impasse is perhaps her iconic skill, and whilst conditional-immortality is great, protecting yourself from damage might not be the number 1 usage. Imagine an Alistar-support lane. Do you target their carry, or Alistar? Immune to the carry's damage, or immune to being shut down? Target the jungler to secure a get away? Sneak a cheeky kill when your enemy flashes to avoid a killing blow, only to die from the damage caused by severing the leash?
Quorra the Aegis of Ionia
|(Innate): Quorra gains bonus Ability Power equal to 20% of the Attack Damage and 10% of the Ability Power of nearby allies.
|(Active): Quorra deals damage to all nearby enemies. If Pulse damages an enemy, Quorra gains an arcane stack for 6 seconds. For each arcane stack, Pulse deals 10% additional damage and costs 7 additional mana. This stacks up to 20 times.
Magic Damage: 50 / 70 / 90 / 110 / 130 (+0.35 per ability power)
Damage at 20 stacks: 150 / 210 / 270 / 330 / 390 (+1.05 per ability power)
Minimum damage to 20 stacks: 2100 / 2940 / 3780 / 4620 / 5460 (+14.7 per ability power)
|(Active): Quorra creates a beam between herself and an enemy champion for up to 5 seconds. Whilst the beam persists, neither Quorra nor her anchor can damage or negatively affect one another. If the beam is broken early, the enemy takes magic damage.
Cost: 85 / 90 / 95 / 100 / 105 mana
Cooldown: 19 / 17 / 15 / 13 / 11 seconds
Magic Damage: 80 / 125 / 170 / 215 / 260 (+0.7 per ability power
|(Active): Quorra places a protective shield on an ally or herself that absorbs damage for 4 seconds. Whilst the shield persists, nearby enemies are slowed. The slow is treated as being sourced from the wearer.
Cost: 60 / 70 / 80 / 90 / 100 mana
Slow: 30 / 35 / 40 / 45 / 50 %
Shield Strength: 80 / 130 / 180 / 230 / 280 (+0.7 per ability power)
|(Passive): On casting an ability, Quorra gains immunity to silencing effects for a duration.
(Active): Quorra decrees a moment of silence, instantly silencing all enemy champions on the field.
Immunity Duration: 1.5 / 2 / 2.5 seconds
Cooldown: 180 / 160 / 140 seconds
Silence Duration: 1.8 / 2.4 / 3 seconds