Yeah, this is almost certainly a Wish thing. Maybe a Wishborn thing in particular too, but this just generally falls into the broad bucket of "relinquishing control", which is something Sabrina is bad at, and relinquishing control over grief in particular, which conflicts with her wish even further.
....Actually.
Maybe that's
exactly it.
I mean, yes, I don't think it's wrong to suggest that Sabrina is a little bit grouchy at being made possibly-unnecessary in the long run. But it's not just that, it's the specific
mode of the technique -- because essentially, the technique is exactly
disposing of Grief by losing control over it.
The technique starts with Grief embedded in your magic -- part of your soul, part of
you, and implicitly going where you go. It's contained and bounded and controlled, it's just in a place you don't want it.
Then you go hand it to someone else, and they hand it back, and you do this again and again and again faster and faster until you
lose your grip on the Grief. The Grief slips from your grasp, and falls out into the universe.
And this, on the broad scale, is doing what you want -- moving the Grief out from somewhere you don't want it, to somewhere you don't mind it. But in the
details, it's a technique where everyone involves forces themselves to
lose control over their Grief, allowing it to slip away. It's fundamentally opposed to Sabrina's Wish, even if the end result is what she wants.