If only Avalon was still connected to her prana, but Saber had become too corrupted and that connection was severed. Irisviel simply kept the sheath safe... and it made Saber feel better to know it was with the woman. And that woman was the only matter of business she needed to bring up.

"Yes, one thing. And this is only because I feel the need to voice something I know I should not need to," Saber replied. "You will treat her well. You will give your life to protect her if you must. If she requests it, you will be her knight again." Saber locked the emotion from her eyes then. "Despite your poor decision, you are still untainted. She should be with you - not me."