Because she has no mind of her own? From what you're saying, she had no business on the force in the first place.It is interesting to think about this Amber Guyger scenario from a few different configurarions:
1. white male cop, young black male victim
2. black male cop, white female victim
3. black female cop, white male victim
4. white female cop, white female victim
I suspect the underlying atmosphere of the department was that females are inferior cops.
She was a new cop as I recall. It is entirely possible that Guyger was influenced by a need to prove her ability to use lethal force. However, that should be seen as a problem with the department and hostile work environment, not entirely her fault.