I AGREE, I WAS EVEN SHOKCED BY ITTT.
But I believe she was a human before she mutated to a monster completely which breeding was possible
She was most likely a regular human then she had gotten sick, becoming a bug while pregnant
So....if you've followed the dialogue mister said, he says that kapar lost her mother due to monsterification process, and in the scene where we see her, I think she filly turned during labour and so and so
Ohh
I just can’t get over the fact that he bred a cockroach don’t get me wrong, kapar is so precious, BUT HOW THE FUCK DO YOU BREED A COCKROACH unless she was human and turned into a cockroach later