Dara was the first of her line to bear all the marks of humanity. Given that her grandmother (or mother, depending on what theory you subscribe to) was the child of Benedict and Lintra, that starts the line at half Chaosian and half Amberite. In order to filter out the Chaosian blood and bring forth a shapeshifter capable of bearing a human form as a natural form, that implies not introducing more Chaosian blood to the mix. Given that it was a breeding project, I wouldn't expect them to dilute the power of her blood with shadow genes. Which makes one wonder... who the hell was Dara's father?
Benedict was half chaosian. Lintra of full chaos blood. (There are those persistant rumors of Cymnea being from Chaos—don't believe it—Chaos took a long time to find Amber.)
So we come to Dara, some few generations removed.
Again I fall back on style instead of substance. The blood is important, but Dara's comment is more about upbringing than genetics—more about structured isolation than blood.
The Chaosian blood isn't filtered out because IMC no Chaosian would knowingly mate with a lesser species, including shadow folk. Instead, Dara is born of House Hendrake blood—and is raised out of the normal Chaos venue. She is given a non-Chaos environ from the time she is small. She is stymied with spells from shaping until instruction forces her intellect and reflex much closer to Order.
Only then is she given more traditional Chaos powers and privileges. We later see much the same done to Merlin. Raising him in fast-time shadow environ isolated from normal Chaos life until he is much more than a child—but not really an adult.
Dara and Merlin are crafted weapons. Dara is too clever by half and she turns on her keepers. Merlin is just shy of idiot savant and he is handled differently.
You could read Dara's words this way, "I'm the first of my line to cling to humanity rather than adapt to the forces of Chaos."
The implication is that Chaos failed many times to construct such offspring before going to extremes with Dara.