How did laura become a cripple and when?The Glass Menagerie by Tennessee Williams
In Scene 7 of The Glass Menagerie, as dinner has just finished, the lights go out because Tom has not paid the electric bill. So, the family and Jim rise from the table and go into the kitchenette. There Jim checks the fuses for Amanda but, of course, they are fine. In the dark, Jim tries to give Amanda a hand, but she refuses, telling Jim to keep Laura company. In the parlor Jim invites Laura to sit with him on pillows on the floor; they engage in conversation although Laura is painfully shy.
As they talk, Jim recalls the sobriquet that he gave Laura in high school: "Blue Roses." This name came about because he misunderstood the illness that Laura contracted; namely, pleurosis:
JIM: Aw, yes I've placed you now! I used to call you Blue Roses. How was it that I got started calling you that?
LAURA: I was out of school a little while with pleurosis. When I came back you asked me what was the mater. I said I had pleurosis--you thought I said Blue Roses. That's what you always called me after that!
A more familiar name for pleurosis is pleurisy. But, the condition is an inflammation of the pleura lining of the lung cavity. Evidently, Laura also suffered from some disease that caused her one leg to be shorter than the other.