Airachnid is from a different timeline called Shattered Glass where the autobots are evil and the Decepticons are good Airachnid lost her sister due to her timelines Arcee infecting her and Black Arachnia (her sister) where her sister died by giving her the antidote Her jack has a white shirt on and goes by Zac to not be confused
Arcee is from the original timeline where her timeline Airachnid kidnapped her and Tailgate then killed him which made her very Protective her Jack as a brown shirt on