Turn kayle's heal into a shield.

That way when you do manage to harass her for not clearing the entire wave in one E, atleast the damage will actually stick.

I realize that in making it a shield, it would not be susceptible to reduction via grievous wounds.

I think this is a perfectly reasonable tradeoff. Her theme is based on saving allies anyway, herself or otherwise. A shield is better for saving an ally than an equal value heal assuming the incoming damage just barely destroys either of them because the shield can't be reduced by grievous wounds. This is fine with me, it fits her identity.

I don't think she should be able to spam her heal in lane and shrug off any damage you manage to put on her though. That doesn't jive with who she is or what she is all about.