Assalamu alaikum ustadh. Can a sister have her brother on her mother side be her Wali for marriage; if she do not have a farther in her life? Her mother ran off with her when she was a baby, so the father does not know of her. Resulting in her not having a father side. P.s, they have different dad

Ustadh AbdulAziz al-Haqqan

Your father is your wali normally as for family complications sometimes they are not an excuse.