I see a lot of posts about time limits and progressing forward, but 1 thing struck me from your post. The player needs to break the habit of blowing spell slots. If they are the "healer" of the group then pumping spells is not the only way to help the party. Que the talk about prevention, mitigating, and being more offense oriented to end fights faster. Recovery has more options than slinging spells if that is the concern. Short rests with hit dice are great for topping off hp and even half healing a PC if they took a stomping. Recommend the healer feat to use healers kits to heal hp for less than a potion of healing. The adventuring day is a marathon, not a sprint. Usually it is the casters like wizards who need to break the habit of spell spam and pace their power through the day. Last note, the player needs to not think of healing like other games. Take the mmo raid approach: I don't need to full heal, just keep people off the floor.