Using 'do a disservice' often includes personal judgment, which can vary by individual perspective. Claiming she’s not ready for the promotion may do her a disservice.
Pro Tip 2/3
Negative Connotation
'Do a disservice' implies a negative impact, whether intentional or not. He did me a disservice by commenting on my work without understanding it.
Pro Tip 3/3
Potential Harm
The phrase suggests actions that could lead to someone being viewed less favorably. Spreading unfounded rumors does a disservice to her character.