@Madcat6204 Yeah I know, this joke's been made since Momo's first "brainwashing" lol
Brainwashing implies forcing your will or an order on someone. Shamiko did neither. She cleared Hon-san's "bad mood" sure, but that could have been achieved any number of ways and just because this made it easier to have a reasonable talk, you really can't pretend that Hon-san wouldn't have listened to a conversation in the real world beforehand. If Mikan and Riko hadn't attacked her like a couple of savages, she would have definitely talked it out with Momo and Shamiko as long as Riko wasn't there to taunt her.
Shamiko did do nothing more than talk to her. She didn't manipulate her or force her into anything, she just got them into a position where they could calmly discuss it. Her powers had no affect on Hon-san's decision itself. If Shamiko had manipulated her mind into making that decision or forcing her will on Hon-san, then that would be proper brainwashing. This was not much more than counseling, which incidentally is more accurate to what Shamiko uses her power for.
Your moral question would only apply if that's what she did, which it is not. Calming someone down is not brainwashing in any sense. At best you could compare it to anesthesia. The decision was completely in line with Hon-san's personality and thoughts, she just was able to think properly instead of fighting for her life.
@KZO
For someone who is allegedly an expert you have a very poor understanding of what brainwashing is. For instance the literal washing of the brain is supposed to mislead you in the first place, it's not supposed to drive the point home. If you didn't get that, then I hope you will in the next chapters.
Also many of her suggestions were not signified by brain cleaning at all (Momo disliking the scuttling of Neo Ancestor Mk. 2 or buying cola).
@Evron
... BTW, Momo began to heal after Shamiko's "brain wash"
That was not necessarily because of her mind getting cleaned up though. Momo was already on her way to healing because of hanging out with Shamiko and finding a lead on Sakura. I think people overestimate how much that clean-up really influenced. It made Momo's nightmares go away, which helped her be more relaxed for sure, but it didn't alter her at all. She would have become attached to Shamiko either way, because of her actions.