I'm not familiar with the story, please elaborate
She refused to allow an investigation and at that time it was customary for the military to honor the widow’s wishes.
There is actually a lot that has been uncovered in recent years that put the whole Hollywood version of Custer’s last stand into doubt. Most recent was a document uncovered in an archive that basically says Custer was free to attack at will. Supply lines stretched far further than Custer was comfortable with. Army ordinance dept sent them with unfamiliar single shot rifles so they wouldn’t waste ammo. Copper casings that swelled and stuck in the breech requiring that they be pried out with a knife after firing. Wildly conflicting accounts from the indians leave plenty of room for doubt. Evidence still found on site that doesn’t match what history says.
Looks like mistakes were made further up the chain of command and Mrs Custer’s decision to prevent an investigation was used as cover. The fact that he had a reputation of being a loose cannon didn’t help his case.
Over all, he made mistakes like ditching the heavy artillery but he was a good soldier who cared a great deal about his men. (See the photo at the bottom of my FR homepage)