Diyoza might have gone back on her deal, but she's very strategic and seems like a smart person. She seems to think things through like a proper leader, even if she's antagonistic. And there's humanity to her, too. We got a tiny bit of that with Dante, but then eventually even when Clarke tried to reason with him, he went back on that and let Cage do what he wanted.
I think Diyoza has valid reasons for reneging on the deal. One of them was probably seeing the fighting pit and being like... no way can we live with all these people who have their own drama and rules. On top of being way outnumbered, even if they get the prisoners down from Eligus IV - 290 (give or take: Kodiak, "four of ours are dead," Madi killed a few, plus the one McCreary just killed) vs. 814??? Not a chance she's going to take.