Heal power is not the only gear used to boost your heals, skill dmg and attack dmg also boost your heal power.
This is what they boost :
Skill dmg: sunspot
Attack dmg: Ceremonial Sacrifice, Stellar Ritual
Skill dmg: riptide, geyser, wellspring
Attack dmg: -
Skill dmg: biosynthesis (self heal and area of heal), fungus among us
Attack dmg: mikollopria
Skill dmg: vital peotocol (only)
Her legendary is only boosted by heal power
Skill dmg: support drone, to the rescue
Skill dmg: rift shield healed
Neither skill damage or attack damage boost his healing chair.
I hope this is usefull for anyone starting the hard job of keep youe team alive.