She is certain of the fact that she has to help Riku. Get him out of this illusion; help him… to indirectly help Sora (who she pretends to feel she owes).
It pseudo-hurts her. She knows the Nobody who cast the illusion, has spent hours on end with him. She had "loved" him, as much as it was possible for one like her – maybe, just maybe, he did as well.
But, right now, it's Riku she has to help. She owes Sora that, owes her savior-to-be the rescue of his best friend, owes him his altered memories. Right now, she is torn… but she knows, hopes that her illusionist will come back to her. He'll take a portal, reappear next to her.
Riku rushes out from the spell, wounding his opponent. Naminé watches, hidden out of sight and out of anyone's mind. Both males battle, darkness lashing out wildly, pages swirling, the glint of blades.
They have him cornered, his magic exhausted. Naminé wishes she could run out and cast a Cure spell, but here she is nothing more than a projection.
"It's over, Zexion". A stab, a cut off scream… swirling darkness. For a moment, she thinks that he has faded; then the dark fully coalesces into a portal and he is off "safe". She has to run out, ascertain that her Zexion is truly alright. No potions on her person, but certainly something that is similar to caring, and she is fairly confident that she can pull off a healing spell or two, possibly fix his cloak.
Somewhere else, in Castle Oblivion, a portal reappears. The same Nobody that had battled Riku stumbled out, struggling to reach the wall and right himself, cursing the boy's proficiency at manipulating the darkness. He fingers a charm that hangs within his cloak, checking it to ensure that it is not broken. The memory witch had given it to him – a show of pretend love. And while neither of them could quite feel, he remembered thanking her and placing it within an interior pocket of his cloak. They were admittedly close, and while the entrance of both Keyblade wielders into the castle had drawn them apart somewhat, they'd both still see each other.
Still trying to catch his breath to open another portal, to get himself somewhere safer than just a corridor (maybe the library, maybe the room where she is kept), someone else arrives. Two someones. A tall male with a mane of flame and poison-green eyes (Axel?) , a somewhat shorter figure who resembles too much the person he just fought.
A couple of words. That is all it takes for the red-haired figure to send the Replica to end him. A moment, and he is being drained, fading. He struggles in vain, then stays too still before completely dissipating into a dark mist which was not a portal.
"Sorry Zexion. You just knew way too much." Axel refrains from laughing, but it is evident in his voice. A small glimmer catches his eyes, a glimmer from right under where Zexion was not a minute ago. A charm in the shape of a misshapen star.
He picks it up – Naminé would know why did the late Nobody have such a thing in his possession. A portal, and no-one is there anymore.
She sees Axel enter her prison, and is "thankful" that her visitor is a kind person. However, she is still waiting for a certain illusionist to make his way up here. Too much time has passed no, barely a couple of minutes, you saw how he barely managed to escape, he still isn't here. She is knocked out of her reverie by Axel's voice, by the drop of a charm that she hoped that was still held by someone else. No, this… where? Why? Zexion?
She shakes her head, scrambling to snatch the star-shaped object away from Axel's hands, checks it for the tell-tale signs of violence – yes, a couple kinks from battle, but none too strong. Who killed him? Took him away? The answer is there, inquiring her. She barely manages to shake the questions away, thoughts tripping over each other broken promises, memories.
Later on, she'll still be aiding Sora. She'll take Riku's side, fix his friend's shattered memories. She'll try hard to help Roxas, Xion and Axel as well. She knows, is sure of the fact, that DiZ will later eliminate her, that she will merge with Kairi.
But, when no-one is looking, she'll finger a misshapen star-shaped charm. She'll recall conversations with a slate-haired nobody, maybe remember the occasional embrace or kiss they shared. Blame herself for helping him fade… then chastise her own mind by even thinking that she would have forsaken Sora - he'd been too kind to her, genuine… but Zexion too; Sora deserves his happy ending, neither of you did.
In the end, when she is whole again, she'll be thankful of the choices she did – she got her heart back, in a way. She just did not get the person with whom she wanted to share this.