You're right, of course, they have no reason to care about their own.
For one thing, she's trying to explain her situation to her sister in simple terms that a kid would understand. But I'd argue she does know the reason they don't care - and it doesn't really change much in the grand scheme of things. A small hive of bees can kill you despite the fact that they're tiny and die if they sting you, because they don't care if they die and have that hive mind. The solution is, of course, not to go poking beehives if you can help it, because they're pretty docile otherwise. But we're not talking about bees, we're talking about murderous tentacle cthulu monsters from outer space. Most intelligent enemies, you can beat up until they retreat to fight another day. Even crazy humans with a cause will run from a losing battle if given the chance. There's no way to "push back" alien forces.
Similar shock issues came up with kamikaze and suicide bombers IRL, using religion or honor or what have you as their "hive" mentality. Just wrapping your head around how to fight something like that is crazy, even if you're aware of it. It's stressful.
It's also established in early game that the aliens themselves are horrific enough that the hardest soldiers of our world and our wars will panic despite years of training under stress, so if we're talking realism... XD
I'd also argue that by definition clones are their own people and have their own feelings, but that's another conversation lol sorry for wall of text, I enjoy picking apart cosmology stuff.