Coworker has no authority to change schedule got confirmation from management she can no longer do this.

My coworker has some questionable traits and qualities for work ethics. She seems to like to change my schedule weekly and I got confirmation from management and our department lead that she has no authority to keep doing this. She is only doing this to my schedule. She does this frequently to cover her rear when she realizes she'll be alone on load day or if she wants to call out the next day (she has high call outs). When do I file a grievance against her for this? She'll get a warning from me that she can no longer continue to modify my schedule weekly without approval. I'm a little peeved that the scheduler is allowing this. Many times she just goes straight to the scheduler to make the sudden change. Frequently without my consent or last minute without the appropriate 48 hr change of shift notification. Usually it's like in the last hour of her shift. I will let her know today or when ever she attempts to modify my schedule she can no longer change it. When do I proceed with a grievance against her? She only does this to me none of the other 5 team members.