Summary
On a return trip from Lothlorien, Celebrian, Elladan, & Elrohir are waylaid by goblins. This is the explanation of why she is not present in Rivendell during the time of the Hobbit, as prompted by J. R. R. Tolkien himself, who mentions Celebrian's capture and torture in the appendices of the Lord of the Rings. I'm rating it M just in case, although it might be a high T as is.