Considerate. Thoughtful. Selfless. Dedicated. None of these describes Myrtle.
Myrtle's life revolves around herself, though not in an intentional or malicious way; she merely sees everything in terms of how it affects her. She has some justification for thinking of herself as the center of life at GMSA, as she is the only one who can write Human - thus it falls on her to order the supplies which keep the others fed and healthy. The fact that she often has to be prodded to perform this duty only reinforces her feeling of importance.
Myrtle lives her life vicariously, either by watching TV or by interfering in the lives of her fellow farmmates. When her TV addiction becomes a problem, Randy convinces her to try taking up some hobbies (like writing)....
Myrtle does manage to think about the others from time to time and tries to do something helpful, but mostly from the standpoint of keeping them happy with her. Her other "helpful" acts are triggered by her maternal instincts, which strike like lightning when the others least expect it.
There's more to Myrtle than meets the eye. And less, too.