Fated Consort by Viola Grace

Two hellish years after the asteroid hit Earth, Mercy and Mender stagger to a pickup point and get taken to the education station. They get medical care, education, and languages. Mender goes through a few queries while Mercy is in medical, and when she is out, he comes to her with the offer. After discussion, they decide that he should take the offer, and he does, but she has to remain with him. It’s his addition to the contract. Then, they wait.
Two years later, her brother is on his way to fulfilling his contract, and his breeding partner decides that she is a drain on resources. He has her hauled to the bond auction with an eye to putting her up for auction before her nephew is born.
On a whim, the assessor decides to re-run her compatibility tests due to her physical condition when she arrived, and to his delight, she is now companion-class. The first step is to offer her to the overseer, and he announces that he’s on his way.
Mercy serves tea to Overseer Usatho. He looks her over and agrees to offer her a bond contract. She gets to stay on the planet that her twin brother calls home, which is really all that matters.