It sounds bad but I can understand Aemond's frustration with Helaena to an extent. Her dragon is the second oldest the Targaryens have and there's even a deleted line from Season 1 where Aemond complains that Helaena "never bothers" with her dragon. And Helaena's just so inconsistent about just how aware she is of what's going on around her, I don't think it would be unfair to think that maybe she does know what's going on, and how much danger they're in. In which case, the fact that Helaena didn't flee or protest would mean she chose that faction and is now sitting on their second best weapon that also happens to make the opposing faction see them as more of a threat and somewhat motivate them to come at them with more force.
Or maybe the writing is bad. I don't know.
Aemond's perspective on dragons and their connection to them is a very limited one. He may be seemingly clever or even wise to some ("philosophies", being able to speak high Vlayrian in contrast to Aegon's terrible use of it", his eagerness to strategize), but his idea of dragonriding is too battle-and-war-centered. He doesn't seem to value Vhagar past her experience and size and use for battle, I'm saying. Even Aegon shows his love for Sunfyre...even it's immediately before going out to try to "prove" himself to anyone. They both appear to only draw strength from their dragon "ennobling" their right to rule or be "important" within this patriarchal Targness war-making that validates them as kings or rulers.
Therefore, it's very possible (bc of bad writing we don't have context for why or why Aemond doesn't observe/put much stock or deep thought into any observations he has of his siblings in other settings to make a definitive conclusion of that based on the "text" of the show) for how Aemond does/doesn't think of why Helaena might be so "subdued" or why it appears she makes "less" use of Dreamfyre or doesn't "prepare" her for war...at least in recent time. And for Aemond, for years Alicent & perhaps Otto have imparted to him and his siblings that they all had to remove Rhaenyra from the heirship/throne, even to survive. A false notion, btw, but one nonetheless Alicent told them for years presumably since early childhood, so yeah, Aemond grew up thinking of dragons as their main line of defense and offense. thus dragon are more war machines to him.
So to both young!Aemond and now!Aemond, "bothering" with a dragon has to do with actively flying them and thinking of them as animals put to a sort of contracted "use". Perhaps just the flying of the dragons is construed by young!Aemond and now!Aemond as "preparing them & yourself" for war. I think that there appears an idea that Helaena--thru her magic in the show--is the most "in tune" with her dragon than anyone on her side of the family. So she absolutely "bothers" with Dreamfyre.
If this were a better written show, we'd see season 1!Aemond also seemingly make as if Helaena doing this is bc women are not expected to battle or that she is "weak"....which contradicts what he expects of her now in season 2/3. That'd be a great depiction of the double standards of sexism the show could have used. (That was a digression, but an important one I think.)
The other thing is that Helaena never asked to be Queen or to have her kid murdered after AEMOND chased & killed Luke and the blacks seemingly retaliated and tried to get at Aemond. (Of course, this is me just taking the show at the moment and at face value and being diegetic bc that's what you seem to ask for). She never usurped Rhaenyra and put their entire family in danger in the first place. Or "distracted" Criston Cole from his post.
That Aemond is demanding that she now go into war:
with no battle experience whatsoever, not even any military training or swordsmanship
when she can barely walk around the Keep without being too overstimulated and is pretty unequipped to also handle war even when flying above it
on a dragon who also has no battle experience whatsoever to possibly deprive her only child of a mother--a girl her father ignored and her grandmother might also ignore with her track record (yes I say this even as we saw Alicent in the leaks say she would take Helaena and Jaehaera away, Helaena: doesn't know of that; has little real reason to trust Alicent after what happened to Jaehaerys; when she made her marry Aegon; and they never were close anyway)
Now he demands that she put her life on the line for something she has no belief in and never had any room to decide on or give input on? when no one cared about her or her kids' thoughts about the whole thing? When Alicent, Aegon, this entire institution has used her body for their own ends? Aemond is entitled to her body and her dragon--the one other thing that she maybe loves above all else besides her bugs and children, a dragon that maybe keeps her settled with herself at heir cramped and oppressive home as much as other Targ women's dragons did for them & be ways/reminders of freedom and personal strength?
Helaena does know...but why should she feel obligated to fight when she is not responsible or did really anything to make the blacks seek out their deaths? no, she didn't "choose" the greens' side even if people argue that she could have fled the Keep with her kids to Rhaenyra. She likely stayed for the same reasons as other women and girls stayed with those who mistreat them--it's pretty much all they know.
However, bad writing also has something here, as we don't know the full extent of Helaena's limits, which could have been revealed if they had taken their time and given us the greens/blacks lives in their respective homes at different times to explore these characters and their relationships...it's also possible that she can't fly Dreamfyre for long, esp with two other kids with her...Dragonstone to KL and vice versa is pretty far even for a dragonride.
I forgot how Helaena, to challenge him abt the consequences if she were to go against his will and say no again, pts out Aemond tried to Kill Aegon already when he asks her again to fly out with him. So, again, she owes him nothing when he'd so easily think of killing herAS WELL AS AND IN CONTEXT OF all the above in this post.
Also, even if we argued for her complicity in the usurpation, it doesn't mean that this would erase the compulsion to stay having no where else to expect to stay and survive on her own.