The injury from the blast was on her back, so the application of the salve makes sense.
Kinda agree that something mythical would have made more sense and looked cooler, but maybe Michael was dumbing it down for the audience...

And I think given the context of the last 'few years' Mac being the more concerned party makes sense to me, especially with Michael's trademark coldness when it comes to his actual daughter.

I saw the scene as a balance of his spiritual and clinical sides.