Well Kayle have the full support package
1) slow
2) heal and movespeed for your adc
3) the low cd ultimate that prevents any dmg
4) your passive reduces Armor and MR from your Enemies so that's better dmg for your adc
The early stage of the game must be defensive cause you are too squishy and you don't rly have an escape . But after lvl 6 you can provide your adc with anything he needs to succed.
And she is also a great counter to assasins.

Pros + Heal + ms in 1 buttom + Rly small cd ultimate that prevents all dmg + Reduce Resistances with passive

Cons - Squishy - Weak Early - No Hard CC

PASSIVE ABILITY

DREAD (Passive):Kayle's basic attacks against enemy champions reduces their armor and magic resistance by 3% for 5 seconds (stacks up to 5 times).

Q

RECKONING (Q):Blasts a target, dealing 60 / 110 / 160 / 210 / 260 (+60% of ability power) (+1.0 per bonus attack damage) magic damage, applying a stack of Holy Fervor and slowing its Movement Speed by 35 / 40 / 45 / 50 / 55% for 3 seconds.

W

DIVINE BLESSING (W):Blesses a target allied champion, healing them for 60 / 105 / 150 / 195 / 240 (+45% of ability power) health and increasing their movement speed by 18 / 21 / 24 / 27 / 30 (+7% per 100 ability power) % for 3 seconds.

E

RIGHTEOUS FURY (E):Passive: Kayle's basic attacks deal 10 / 15 / 20 / 25 / 30 (+15% of ability power) magic damage on hit. Active: Kayle harnesses her righteous fury to increase her attack range by 400 for 10 seconds. These attacks splash, dealing 20 / 30 / 40 / 50 / 60 (+30% of ability power) additional magic damage to her target with nearby units taking 20 / 25 / 30 / 35 / 40 % of her attack damage plus magic damage. This splash damage does not affect turrets.

R

INTERVENTION (R):Kayle bathes a target ally champion (or herself) in a holy light, rendering them immune to all damage for 2 / 2.5 / 3 seconds.