From the reporting I read she'd not yet technically been discharged when she went on the march, so still potentially subject to military justice, court-martial, etc.
I'd say one would be a persistent pattern of behaviour following her earlier reprimand, i.e. attending another dubious protest while still on active duty, prior to actually leaving the military, probably effectively ignoring the reprimand. I can't see that going down too well in the army.
Also the US Army Captain who was at the event has resigned her commission
https://twitter.com/DavidBegnaud/status/1348619052139175936