War induced childhood trauma, indoctrination, religious fanaticism, narcissism, god complex, delusions of grandur, severe depression, obsesion with control, sadistic tendencies, abuse of authority, religious extremism, conspiracy, treason, literal heresy and blasphemy, ... having an unhealty desire for his sister is the lesser of his many problems at this point... and ours.
I'm guessing she had the sudden realization that she has indeed changed, which brought her happiness (hence her apparent tears of joy). Apparently Kafka and the Trailblazer are destined to change one another; and achieving such change is one of Kafka's main goals.
She's got a major case of brother complex, so it's not so much no one would choose to marry her but that she'd flat out turn down anyone who'd be interested.
