Absolutely! Aarya could have better thought about human, but it just 15 years, it's nothing compare to millenia years of war! They could only hate human less at best! And with the news of such a betrayal, how could they take it so... well? Even Emrys first thought is revenge! But I can understand why Nidhoggr didn't dare to bring up about her child to Aarya. She's scared of their reaction and maybe her daughter and her husband safety if they learned about it, consider how much Aarya hate human back then, and Shawn is the result they get from killing Lucius whole clan. I think that's also why she tried to change Aarya's opinion about human first before let them know. That's more about how you know someone well enough to predict their reaction and want to handle it the best you could rather than trust issue to me.
It's more about inconstancy. And she miscalculated. She expected Aarya to take her union with the homunculus and her daughter so badly, considering she wasn't some stranger, while Aarya had absolutely no problem with humans when they were alone. Narrative logic died somewhere here.
Everything looks as if Nidhogg died by accident and Harald simply decided not to let the good things go to waste. And when his action was revealed, he was like “oops, sorry, but I really needed that.” In this case, I would probably really just shrugged, but we are dealing with premeditated murder.