Mother of Arthur Weasley.
Cedrella's marriage to Septimus Weasley caused her to be "blasted" from the Black Family Tree (see BFT and my notes).
Spouse: Septimus Weasley (see BFT and my notes). Septimus might be the grandfather that gave Ron the Wizard Chess set (PS12).
Parents: Arcturus Black (1884-1959) and Lysandra Yaxley (BFT).
Siblings: Callidora (Longbottom) and Charis (Crouch) Black (BFT).
Children: Arthur Weasley (Feb. 6th 1950-) Arthur had 2 brothers (JKR); Ron's namesake uncle Bilius (PA6) may be one of them (he could also be an uncle on Molly's side). According to Jo, Ginny is the first female to be born into the Weasley family in generations, so we can deduce that Arthur had no sisters (JKR).
"Cedrella" may be a form of Cedric, or possibly related to "Cinderella" from the fairy tales.