He had vanity, which strongly inclined him in the first place to think she did love him, though she might not know it herself; and which, secondly, when constrained at last to admit that she did know her own present feelings, convinced him that he should be able in time to make those feelings what he wished.
She was so little equal to Rebecca’s puddings and Rebecca’s hashes, brought to table, as they all were, with such accompaniments of half-cleaned plates, and not half-cleaned knives and forks, that she was very often constrained to defer her heartiest meal till she could send her brothers in the evening for biscuits and buns.
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.