The alarm bells at her first appearance screamed "River Song". Not sure if they are correct, but the last thing we got out of the River that was in the Library computer was "spoilers" in relation to Clara's survival from jumping into the Doctor's time stream. Also River definately not wanting either Clara nor the Doctor to jump in there. To the point she tried to slap the Doctor even though he shouldn't be able to notice her or feel the slap. Either she thinks they'd die...or she knows what's going to happen (in someway to some event we may not have reached yet).