Other Beth is a refrigerator located in the medical bay on the Galaxy One.
Like Beth, she is just an ordinary refrigerator, but Gary treats her as if she is a living being (or at least an intelligent robot). In "Chapter 2" he admits to Avocato to have had some dark conversations with her, and that she knows "everything".
She was destroyed along with the entire Galaxy One in "Chapter 10". She was blasted to bits by a shot from the Lord Commander’s ship as Gary prepared to ram it with the Galaxy One.