Tara shot herself in the foot by basically coming up with the idea, pitching the idea as purely her own, and really not delegating anything. If the task had been about certain aspects of the task such as painting, or design, or marketing it, then you could shift blame, but this was all about the basic design.
If it had been about art, then I think Tara had the right idea. The Magna billboard seemed shoddy in terms of quality, and the writing was absolutely terrible looking. But, it showed all of the Vistas of the normal game itself, while combining it with the "We need Street Cred to combat NFSU2" aspect of their marketing plan.
Tara owned this task, but not in the good way. Her idea, her pitch, her failure, her firing. It was simple, clean, and not surprising in the least.