The Ezekiel quote is the major reason.
But of course, Mary is associated with the dawn (because she experienced Christ’s salvation in her life before the Cross had even happened, and because she’s a sign that humanity is being made new).
Also, the Bible tells us (in the OT prophets, mostly) that Christ’s Second Coming will come from the east, and the traditional Christian direction of prayer and burial is toward the east. So Mary is associated with the east because she’s associated with Christ, the Sun of Justice.