Like Katrina said (in the bar to Liz), when Auryn went back through the New Church gate to get home, it scrubbed away her vampirism. Katrina also had Auryn's uber-cool sword because it would also have been erased by the gate because it was considered magical (magic-infused). If you're wondering why Auryn didn't  just come back with Katrina and the rest of Lupin's clan, there is a reason for this, which I will get to later.
But, because Auryn was a first Gen vamp (Lillith was the first vampire in my world, arright?), there was still some traces of it left in her system.
Vamp bites Auryn = back to first gen vampire.
There is some ASS WHOOPING TO BE HAD!