In Elden Ring, Renna is the NPC who gives you the all-important Spirit Calling Bell along with your first Ashes, the Lone Wolf Ashes. But meeting Renna is not inevitable, as you have to backtrack a little in order to do so, and the game doesn’t specifically encourage you to do this. The conditions for meeting Renna are that you have received Torrent from Melina, that you go to the Church of Elleh at night, and that you haven’t yet reached Roundtable Hold.
However, even if you meet these three conditions, you might still be having trouble making Renna appear. After receiving Torrent, we rode back to the Church of Elleh, used the Site of Grace there to pass time until nightfall, then waited around until it got properly dark. Renna still did not appear.
In order to make Renna spawn, we had to go to the map and fast travel to the Church of Elleh (even though we were already at the Church of Elleh). This made her appear directly in front of us as soon as the fast travel completed. So, if you’re having trouble making Renna spawn, try fast travelling to the Church of Elleh at night.
If you’ve already gone as far as Roundtable Hold, then it’s too late to go back and meet Renna. However, you can still buy the Spirit Calling Bell and the Lone Wolf Ashes from the Twin Husks merchant at Roundtable Hold.