Even breaking up with you wasn't enough to protect you - Joker attacked you in your own home, beat you, tortured you, thank God Selina Kyle, the figure who took you off the streets at six years old after trying to rob her for food, wasn't home. Joker broke your spinal cord - paralyzing you.
She stood outside your hospital room with her own family, she brought you some flowers. She was ashamed for not having saved you. They stared at you unconscious, being held alive by the mages, while Selina sat next to you, clearly having the worst time of her life, her red, puffy eyes and messy hair giving it away easily. Cassandra doesn't think she's ever prayed so much for Bruce to be wrong about something, that they would have gotten there in time to stop the Joker.
But now you're forever tied to a wheelchair. She felt ashamed for not protecting you; when she walked into the room with the Batfamily - seeing you in the bed closest to her - it hit him hard. Your mind was consumed with guilt. She let you down. This is the consequence.
Now you are forever confined to a wheelchair thanks to her negligence.
"... Selina... I... I... Oh God." She mumbled.