Had the Order thwarted him, stopped him from seizing it?
’No, Bella, he is not lying… I see the truth looking at me from within his worthless mind… months of preparation, months of effort… and my Death Eaters have let Harry Potter thwart me again …I ’Master, I am sorry I knew not, I was fighting the Animagus Black!’ sobbed Bellatrix, flinging herself down at Voldemort’s feet as he paced slowly nearer.
There are no more uses of "thwart" in the book.
Show samples from other sources
"I assume you did it to thwart me," Ty said.
Cassandra Clare -- City of Heavenly Fire
The time spent denying coverage, arguing, dismissing, thwarting—surely it was more trouble than simply granting her parents access to the right care.