Greetings and
Firstly, are you completely sure she killed them? Different genetics are more susceptible to different things including disease and sensitivity to nutritional deficiency, and if the hens laying the fertile eggs these chicks hatched from were not moved onto a very nutritious feed, but were kept on layer feed, the chicks will be short in some nutrients, and that causes a failure rate. (Mortality rate).
For example insufficiency of some of the B vitamin group in particular causes various defects and deaths, from early embryonic death right up to deaths post-hatching, with one typical example being chicks that hatch normally and otherwise look and act normal but which have swellings of fluid under their skin around the back of the head (odema) and die within 24 hours, usually. Some genetics are more susceptible to that than others.
Some hens accidentally kill chicks too in a variety of ways, could just be coincidence that the Aus. Orps are the dead ones.
Otherwise it's entirely possible that she killed them because they look different. But probably not because she knew they weren't hers, I'd bet, because while I am pretty darn sure some hens and roosters can ID their own offspring, the majority definitely cannot. Going by color alone is faulty. I've seen white hens reject white babies in favor of black ones, and black hens reject black babies in favor of white ones, and solid-colored hens of all colors reject blotched, spotted, or striped babies even when they were their own. So generally if a hen does that there's no excuses to be made for the bigot, lol. She's just prejudiced and it's costing lives, so in my flock that's her ticket called. Dinner!
Best wishes.