The "you" in her little line is the big thing. We really don't know what could have been foreseen. The big thing about Mara Sov is that she alone had the ability to foresee some things, but to see Eris succeed against Crota? That's pushing it for me. I'm sure it's the likely answer we came out of that pit with Crota's blood on our hands... but then again, it might be Eris... or the Nine... or maybe even another Awoken we don't know about yet... lots and lots of possibilities...