Okay! More headcannon time! Valentina Furi is a fascinating character, and I'm going to bet she's a little messed up from the end of Secrets Revealed.
So, Secrets Revealed finale, Valentina tries to live up to the Furi Legacy, make her family proud, including Serena. So she 'borrows' steals the Fairy Gemstones from her friends, with little trouble. However, given subsequent events, it's not implausible to imagine that the Sapphires are a tad more cautious when lending Valentina their things in the future. This might leave Val feeling hurt, or filled with self-loathing, because she has only herself to blame.
Secondly, when Serena made all the mind-controlled people give Valentina a round of applause? Not only incredibly creepy, but Val probably has nightmares about that, and can no longer stand hearing people clapping. And given her strong desire to be the best, and getting praised for that, the future could be difficult. Like, imagine she's just done a really technical move on Cinder, and she's the top of her class, and Ms. Furi or Ms Wildwood encourage the others to congratulate her, they start clapping, and Val has something akin to a panic attack, reliving one of the worst nights of her life? Terrible business.
Also, for Serena-related reasons, Val might have a great fear of heights/edges/falling, and given their unicorns now have wings, are alicorns, that might constitute a problem. Also! Val might find singing too triggering for her, which would be a shame.
Anyway, this all comes to a head on Halloween, or the Unicorn Island equivalent, where there's music, costumes, and a free pass to scare people. Rory is in his element, the prankster. So Val's just getting ready, she's a witch, and she stands out on one of the Sapphire Dorm balconies. She can hear music playing from the main hall, but not Serena's thankfully, and there's a bit of a chill in the air. From inside, she hears a clunk, and a thud. Turning around, the lights have gone out.
She frowns, and goes to investigate, when she hears "Vallllenntiiinaaa..." from the darkness. In a groan that reminds her too much of the zombies from the Solera Festival. Someone, Rory or Sophia, appears from the gloom. They're dragging their shoes, limping, groaning, their skin is pale, and their eyes have a malevolent violet glow.
Val screams, backing away, finding herself cornered by the balcony. She takes a step back, onto the raised edge, and slips. She screams again. Her zombified friend snaps out of their trance, and runs to help her. Her shouts also bring Isabela and the other Sapphires onto the balcony. Everyone helps to bring her back onto solid ground, where a shell-shocked Val is numb to the world. The zombie, Rory probably, is apologising profusely, and Ava or Layla is getting her some tissues for her tears. Sophia tries to ask what happened, but Val can't explain.
Isabel knows though, because Val told her afterwards. Not all of it, but enough that Isabel knows that she just needs to get away. So she scoops her up like she did when she was sick, and carries her back to her room. Val's able to calm down after a while, and several cups of tea, and then tells Isabel exactly what went wrong. She doesn't judge, and tells Val to skip the festivities and get some sleep. Then Isabel goes to find the rest of the Sapphires and explains what happened and how they can help.
Okay, that went a bit off track at the end, but the point is, Val has much trauma from the end of Secrets Revealed, and only Isabel can truly help her.
