Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.
Alice read the books in the wrong order.
She’s a little kid, she probably didn’t know which ones were meant to be read first. The world of Odin Sphere eventually turns into Toto Bunny
The Pooka who rejected the cure to their Pooka Curse went on to become a dominant superpower, and with the Netherworld wrecked but not forgotten, Prinnies are born on the planet they died on, and are given special treatment. Gwendolyn and Oswald aren’t actually the last humans.
At least I hope they aren’t cause otherwise the future population would be very very inbred.