Elinor advised her to lie down again, and for a moment she did so; but no attitude could give her ease; and in restless pain of mind and body she moved from one posture to another, till growing more and more hysterical, her sister could with difficulty keep her on the bed at all, and for some time was fearful of being constrained to call for assistance.
There are no more uses of "constrained" in the book.
Show samples from other sources
...it is very grievous to be constrained to keep our hands off such a dainty dish as Narnia.
C.S. Lewis -- The Horse and His Boy
It seemed that we were all cloaked in an unwelcome garment of racial difference that constrained, confined, and restricted us.