Evan spends a lot of her time, once the Gang go to the underworld, at the Convent. She is in no state to deal with the whole mess that is her parents being stuck in Storybrooke, so she hides away, taking care of baby Hood and the others with Blue.
She's there the day Hades has Rumple open the portal. She's the first to realize Blue isn't Blue, and she get's sucked down to UnderBrooke with Belle, Zelena and the baby.
While she's in UnderBrooke, she runs into various characters from Derek and Odette's past, mainly King William and Rothbart.
At first, she doesn't know the kindly old man she's speaking to is her grandfather, be he does. He can see his daughter in this girl's eyes and smile.
But Rothbart, he's very aware who Evan is. He bides his time, watching the Heroes. Then, just before they leave, he uses a bloodmagic of his own creation to tether his soul to Felix's feathers that Evan had been wearing the day she was brought to the Underworld, to make an escape of his own.
But his spirit is weak once they make it top side so it takes him a long time to gain the strength to wreak havoc on the living. So long, in fact, he has to summon Derek and Odette back to Storybrooke for his revenge.
