He could have grilled Zelda some more but it seemed Ib really was serious about taking things into her own hands. Given the courage he inadvertently seemed to have inspired her with, he couldn't very well just let her go in alone and so with a light 'Hm.' followed Zelda in after the girl.

Sephiroth didn't think Ib would get very much further than Zelda herself had done but perhaps his presence in the room might go some way to back her up. If not, then he'd just have to have stronger words with the man himself.