Best of all, the worst punishment a military inquest could mete out in a case like this was dishonorable discharge—although that was unlikely, since she was only an auxiliary guard.  Because of the double-jeopardy clause in Equestrian law, if things subsequently went all wrong, Lyra couldn’t be re-tried, and if they held the inquest quickly—while the creatures were still in hospital—it was unlikely anything would go wrong enough in the interim to change the likely outcome of a trial.  As an added benefit, foreign ambassadors and such couldn’t complain that Celestia was playing favorites, since the trial would be a foregone conclusion before they even found out about it.