"Nasty" is far too subjective. And I really don't see what's so nasty about her in this.
Frankly, this is how Storm should always be written. It was showing her to be scheming, headstrong, independent, etc. She is not someone who is led (EVER); she leads and blazes her own path. That's the only compliment I give this story though.
I haven't read the story but Storm sticking up to Scott and refusing his orders certainly isn't a new development.
They even fought over who should lead the team. She has always had a strong leadership/independence streak.
She also hasn't always been "diplomatic/wise". Look at how she dealt with the Morlocks and her fight with Callisto. She made some pretty tough and "undiplomatic" choices. Also, the changes she went through when she met Yuriko in Japan show that her personality isn't simply calm/staid.