Well she's brave enough to charge the rear of the ships formation which consisted of 5 ships while there still several light cruisers around, anyway it was surely chaotic since it was night, they have smokescreens, and there's the heavy amount of gunfire being exchanged.

She's brave... but not as brave as little Johnston.

Also, Yuudachi's crew were already raising the white flag but Portland ignores it and fed her several shells until she sunk.

Lunatic6 said:

Also, Yuudachi's crew were already raising the white flag but Portland ignores it and fed her several shells until she sunk.

Not entirely true.
However, not far off.

As stated in Kancolle, Yuudachi's captain ordered her crew to 'raise the sails' in order to maintain morale.
However, this looked like a White Flag to the Americans and thus they started ignoring Yuudachi.
Yuudachi then fired on passing American ships, in apparent breach of the Code of White Peace, which allowed her to score her more famous hits and potential sinkings.
The Captain and Crew of the Portland nearby (which had been disabled in Yuudachi's earlier sneak attack), rightfully enraged, returned the favor; all the while filling the air waves with various obscenities that only sailors could understand.
There is an argument to this day whether Yuudachi actually had a legitimate White Flag up or if what Mr. Hornfischer (who wasn't born yet) is referring to were her sails.
However, to this day, in American naval custom Yuudachi is still considered to be one of the most dishonorable ships in history.

Now, this part I can't guarantee, my sources are a little fuzzy about it; but, if they're right, the entire incident infuriated the Americans so much that, for the only time in modern history, US high command actually passed the 'No Quarters' rule (this was deemed appropriate because technically speaking the Japanese no longer fell under Geneva in our books).
Que impromptu sinking of any Japanese ship that they spotted, military or otherwise, and only taking prisoners if they so happen to survive and the crew felt like it.
This rule remained in effect until the formation of 3rd/5th Fleet six months later (Halsey wasn't so much a fan of it).
So, you could actually say that most of the American Navy's harsh war tactics against the Japanese Navy until then were Yuudachi's fault.
...
Of course, as I said, that part is questionable even to myself, but if it's true... ouch.