Oma doesn't want to fight. She doesn't have the strength, or the stamina, or the courage.
Oma wants to heal. So she learns. And every minute she spends learning to heal is time she can't spend training to fight, but they don't need her. They have better prospects.
She practices, and she practices, and when the ships arrive, she has the same sinking feeling in her chest that comes from losing a patient.
She hopes that they don't force her mother to watch her die.