... Her first thing with Harry was more than physical sex, it was something special, a reaffirmation of her claim over him ...
Oh, yes; of course. It was a ritual.
Ritual sex is a Big Deal(tm).
Ritual sex between a Faerie Queen and a Starborn... on the Stone Table, which channels energy???
... but remember Harry's body was still hurt and, if I am not mistaken, their union was a spiritual/mental something something. Harry's body still was in the same place.
I'm pretty sure you're right, although I think it may be fair to say "it's more complicated than that." Standing there at the Stone Table, negotiating with Mab as she stalked around him... Harry was
standing there; i.e. not limited by his broken back.
Mab (as Harry realized) was closing a circle around him.
I think at some point she actually summoned him (physically) into the circle. Probably after she he had him laying on the Stone Table (since he was laying down, back at the church).
She healed him there, on the table: I think his body had to be there, for that to happen. Not even Mab has unlimited power, after all.