A Mord'Sith should love her Lord Rahl.
That's one of the first things an apprentice learns. It was one of the pillars they lived by, a defining aspect of life in a Mord'Sith Temple. Everything revolved around him.
Cara broke through the defense of the D'Haran forcefully. Out of my way. The next one didn't even get to finish the first swing her made at her. She just ducked under his arm and settled herself where she needed to be in this fight.
Richard was fighting a few yards away, but the main point was that there were no enemies between them anymore. She barely registered the scream that she almost pushed out of the soldiers' lungs with the agiel.
Cara saw, felt, danger coming from the corner of her eye, and ran towards it. The D'Harans' eyes were focused on Richard's unprotected back, and the agiel in his side caught him by surprise. As did the Mord'Sith crashing into him, probably.
When she'd gotten up, the battle was over. She saw that Richard quietly assured Kahlan that he was all right, and Zedd slowly walked towards them, sweeping the fallen for any sign of life. She breathed slowly, feeling the rush of battle fading.
A Mord'Sith should love her Lord Rahl. That's why she protected him. That's the only reason. They went out to search for wood for a fire when she felt Richards' hand on her shoulder. "Thanks."
The only reason, surely.