He sent a man to report the actions to the Lord Captain commander. What do you want him to do?

Don't be absurd - they are alluding to laws intending to protect Aes Sedai. They are not referring to any horror of brutality, just an agreement that sisters can't torture ONE ANOTHER. There are no restrictions on what they do to anyone else. The Chair ter'angreal they are going to face penance for using on an admitted Darkfriend just because she happens to be a sister, is routinely used on petty criminals to terrorize them for sullying Tar Valon.

That is possible. However, the only facts we have are that the Aes Sedai have special rules that protect themselves and their potential membership from harsh treatment. The furor over Elaida's attack on Egwene comes not from any moral revulsion against violence, but from the fact that she transgressed against a sacrosanct initiate. In fact, they later point out that an acceptable defense for Elaida is her sincere belief in Egwene's own evil. By Tower standards then, believing someone is a Darkfriend, however wrongly, justifies abuse and violence towards them to a certain degree.