You're very right--there's giving out socially-unacceptable facial tattoos and kicking you upstairs to Sky-And-Sun Land, sure, and that's no good, but this will strike Signy as marginally more horrific than being Casteless, even. There's also a part of her that'd be really fascinated to find out how it happened, and how the Rite of Tranquility works, since it's sort of the polar opposite to Dagna's discovery of how to connect dwarves to the Fade.
(In my own ~imaginary canon~ for the game I kind of think that Dagna figuring out how mages were made Tranquil was a large step in figuring out how to make herself a mage, but that's just me!)