Honor has been studying longer and has that arm that is not bendable like a real arm. Thandi is apparently stronger, but Honor is pretty strong herself. Just her parts of protecting the Protector in HotQ are below. In sparring I think it could go either way as neither will try to kill the other. In a battle to the death, Thandi would most likely have the advantage, except for Honor's holdout pulser.
The Honor of the Queen wrote:
This time she did—and as she also felt the emotions of the fresh “Security detachment” through him, she exploded out of her chair. The heel of her hand slammed into the face of the newcomer closest to the Protector, and cartilage crunched horribly as she drove his nose up into his brain—just as his companion dropped the dispatch case, raised his other hand, and fired at pointblank range into Captain Fox’s chest.
The Honor of the Queen wrote:
She reached out and caught the killer by the nape of the neck with one hand and reached past him to clamp her other over his gun before he could get a clear shot at Mayhew. She missed the gun but captured his wrist, and he dropped the weapon with a howl of anguish as her fingers squeezed and the hand on his neck yanked him off the floor. His eyes started to roll towards her in disbelief as he hurtled through the air, and then she slammed him back over the table. Dishes flew, crystal shattered, and his eyes bulged, shock become agony as the point of her elbow smashed down. It hit his solar plexus like a hammer, driven by all of her weight and strength, and she whipped away from him, leaving him to die as his lungs and heart forgot to function.
The Honor of the Queen wrote:
A horde of fresh “Security” men charged through the door, all armed with disrupters, and Honor snatched a heavy metal tray from the table. It flew across the room, as accurate as Nimitz’s frisbee but far more deadly, and the leading intruder’s forehead erupted in blood. He went down, tripping the man behind him, tangling them all up briefly, and then the chaos became total as the Protector’s bodyguards suddenly realized who the enemy truly was.
The Honor of the Queen wrote:
His victim went down shrieking, and the man beside him swung his weapon towards the treecat, but Honor flew across the carpet towards him. Her right leg snapped straight, her boot crunched into his shoulder, breaking it instantly, and a hammer blow crushed his larynx as she came down on top of him.
The Honor of the Queen wrote:
The killers had known she’d be here, but she was “only” a woman. They were totally unprepared for her size and strength—and training—or the mad whirl of violence that wasn’t a bit like it was on HD. Real martial arts aren’t like that. The first accurate strike to get through unblocked almost always ends in either death or disablement, and when Honor Harrington hit a man, that man went down.
The Honor of the Queen wrote:
She tucked and rolled, taking the legs out from under two more men, then vaulted to her feet and drove a back-kick squarely into an unguarded face. A disrupter bolt whizzed past her, and iron-hard knuckles crashed into the firer’s throat. Nimitz howled behind her as he took down another victim, and she smashed a man’s knee into a splintered, backward bow with a side-kick. He fired wildly as he went down, killing one of his own companions, and her boot pulped his gun hand as she turned on yet another. She snaked an arm around his neck, pivoted around her own center of balance, and bent explosively, and the crack of snapping vertebrae was like another gunshot as he flew away from her.
Shouts and screams and more shots echoed from the hallway, and the assassins turned on Honor with panicky fury while their rearmost ranks wheeled to confront the reinforcements. Someone thrust a disrupter frantically in her direction, but she took out his gun arm with one chopping hand, cupped the other behind his head, and jerked his face down to meet her driving kneecap. Bone crunched and splintered, blood soaked the knee of her trousers, and she twisted towards a fresh enemy as the real Security people broke through the doorway at last.