Katya never had made such confessions to Alyosha before, and he felt that she was now at that stage of unbearable suffering when even the proudest heart painfully crushes its pride and falls vanquished by grief.
There are no more uses of "vanquish" in the book.
Show samples from other sources
The team vanquished all competition.
You need to vanquish those negative thoughts and think about good things.