For starters, we have absolutely no idea what the context of this scene is. We have no idea what action plan Helaena is criticizing. Based on the Dream Helaena had last episode, Rhaenyra could very well be trying to force her to burn smallfolk to protect the Dragonpit. 

But even if that's not it? Helaena has every valid reason to hate Rhaenyra. 

Let's start with the obvious. Jaehaerys. Now, Rhaenyra didn't order his death, but Daemon did, and Rhaenyra had several lovey-dovey moments with the baby killer this season. In Helaena's position, I would hate Rhaenyra for that alone. 

Despite that, Helaena and her Quokka mother made it possible for Rhaenyra and Daemon to take the city without getting shot down by scorpions. They honored their bargain as best they could, and all they wanted in exchange was to leave. Poor Helaena just wanted to raise chickens with her children and live in anonymity. But instead of letting them go, Rhaenyra kept them imprisoned...for what seems to be no real reason other than the fact that they're "Hightowers" (Helaena is a Targaryen). 

She only allowed Helaena to see her daughter every few days, which in and of itself is a cruelty when Helaena already had one child taken from her. And then, she even took THAT away, isolating Helaena from Jaehaera altogether. 

And because that wasn't bad enough, apparently, Rhaenyra starts being fake-nice to her once she learns she's a dreamer (Rhaenyra never once treated her like a sister before that). Then, despite knowing that Helaena is fragile, Rhaenyra starts bullying and manhandling her when she cannot serve as Rhaenyra's Magic 8 Ball on command. 

Any one of these things is a perfectly valid reason for Helaena to hate Rhaenyra. All combined? If I were in Helaena's shoes, I wouldn't have merely made a somewhat-harsh comment. I would have started whispering so Rhaenyra had to lean in, then shoved a knitting needle through her eye. 

Helaena would be justified in hating Rhaenyra