She's mostly just tried setting aside Golarion and thinking about the rest of the universe, the destruction of which is less certain. She doesn't see how Rovagug will be contained in time to save Golarion even with Asmodeus interested in doing it, but that's still a lot of other planets, and all the afterlives, to try to save.
If Carissa were trying to develop a structure for describing the behavior of magic she'd have approached it very differently; she'd have picked the spells that are the oddest-feeling in your hands, the ones that feel slippery or tense like they're barely holding together, the metamagics that feel the most like they strain the original spell, and try to figure out what tolerances, exactly, those are straining, what invisible dynamic they come close to breaking. She's not sure she has anything she can translate into Keltham's terms, yet, but that's what she's attempting.