Some QoL changes Soraka could use

Remove her ability to heal non-champion units, it's just cause for game ruining missclicks where you were slightly hovering above that ranged caster minion instead of your ADC who's about to die.

When a low health ally is outside the range of your passive it should be apparent, some kind of icon with the healing icon or a change to the healing icon itself (for when they're too far). Also when they're outside the range the max range circle should be visible.

Let's say your heal is worth 400hp and you try to heal someone who's missing 300, it will currently take 10% of your max hp, instead it should only take the % of health required to do the heal so in this case you'd only need 1/4 of the given health and so the cost should also only be 3/4 so 7.5% of her max hp in this case.