Might I ask why? Her "connection to mother earth" or something like that? Just curious.
To me it just seemed like yet another bs reason to justify Cassie's presence among the Ellimist's (disputedly) stacked deck. Rachel dies because she was the random member who had no real purpose (Ellimist tells her as much in book 54). The nonsense about subtemporal grounding combined with all her other "miraculous abilities" was the bs way to justify Cassie's presence.
The "stacked deck" thing didn't make real sense to me at all--if anything, Rachel was more *predestined* to be there than Cassie, just because of her attitude towards fighting and how suited she was for it. And tbh, it's been years since I read MM4, but all I remember is the plot careening ridiculously out of control, and then being oddly satisfied with how it was resolved. It's not just *Mother Earth*, it's that Cassie has a deeper awareness of emotions and motivations that, in a sci-fi setting, would lead her to notice things wrong with the universe she's in. It's Deanna Troi's power, and she was always the one to figure out when something wasn't quite right, which was about her only power other than going "Boy Captain, he sure is angry." "Yes Counselor, thank you, I got that when he told us how angry he was."
I didn't like Cassie as a character. She is a huuuuge hypocrite. I just re-read #16 and godDAMN can that girl not make up her mind. "We can't let Fenestre keep killing humans!" "So what do you want to do?" "Kill him!" "Go ahead" "But uh my morph is not suited for it..." But if sci-fi is about blowing all things in normal, everyday life into epic, supernatural proportions, then I believe someone who's generally a little more empathetic and unfocused on the superficial nature of things (no matter how wrong she often was) would be able to tell when a universe is forged.