She refuses to be a surrogate for any alien.

Sarah French refuses to passively accept her fate as a surrogate for a Palantir chief. She has to accompany the beastly alien general to his home world, but she only has to give him a year to woo her and act as his surrogate before she can walk away. Determined not to have a child she has to leave behind, and sure she could never love an alien she hasn't met, she takes an illegal drug that will prevent conception, possibly forever. She just has to endure the year and will be able to walk away with no lingering ties. It comes as a shock to realize Reld is a lot different than she expected (in many knotty ways), and the possibility of a new and happier life on Baxa beckons. With her secret between them, will he be able to forgive her actions and accept just her, since she might never conceive?

Seven years ago, the Faction agreed to save Earth from the Vorathan invasion in exchange for Earth women giving them one year of proxy rights to act as a surrogate, since the aliens of the Faction faced a dwindling population. With the Vorathans feared throughout the galaxy as bloodthirsty, vicious marauders, the Earth's government agreed.

That doesn't mean the women did.