How has Kira been her worth despite having a physical disability?

Kira has been of great help to her mother regardless of her disability, and she has never been a burden. According to her mother:

"Your strong hands and wise head make up for the crippled leg. You are a sturdy and reliable helper in the weaving shed; all the women who work there say so. And one bent leg is of no importance when measured against your cleverness. The stories you tell to the tykes, the pictures you create with words—and with thread! The threading you do! It is unlike any threading the people have ever seen. Far beyond anything I could do!” Her mother stopped. She laughed. “Enough. You mustn’t tease me into flattery. Don’t forget that you are still a girl, and often willful, and just this morning, Kira, you forgot to tidy the cott even though you had promised.”