It has become clear enough that, in search of an answer to your specific predicament- or, at least, Makoto-san's predicament, you should go to visit someone from the Velvet Room.
This, of course, leaves the question of who to go to. Elizabeth is a Wild Card, so whatever's happening could also affect her, but her relative sanity in comparison to her siblings is... not great. So while you'd probably get answers after a while, you'd have a more difficult time understanding her.
There's also Theo, who's presumably reliable, but who you don't know all that well. He's another good option, but...
...So far, every time you've had a big question about Personas, or what to do next you've always gotten your best advice from Lavenza. And you feel like the same could hold true here, as well.
She's definitely the most helpful of the three. Though, it'll be harder to tell once Margaret-san gets here. Really, where is Narukami-san?
...Besides, out of the three siblings present, you find her the least scary. That is definitely a factor here.
"I could ask Lavenza-san about it," You suggest out loud. "She's... pretty good at putting things in ways I can understand." You'd needed that a lot, last year, and you actually think it went pretty well. By this point last year, you were... actually sort of okay. "Maybe she'll be able to help us with this."
"Are you sure?" Morgana tilts his head to the side. "I don't think she's ever had a Guest before. What could she know about this?"
"Probably more than we do." And isn't that the important part?
Mitsuru-san glances at you. "I suppose you'd be able to find her?"
"I don't think she'll have left the Velvet Room," You confirm. "At least, unless she really wants to see the festival." And in that case... she could just wait, and you'd be more than willing to show her around.
You guess that means it's your job to get Lavenza's help. You suppose it makes sense. You're the one that knows her best.
Still, it'd be easier if it was the actual Wild Card doing the talking.
You're not letting the others get away with sitting back and letting you do all the work, so you drag them with you to the Velvet Room. "Lavenza-san, I have a quesiton for you," You declare.
She blinks up at you. "What is it?" It comes to mind that you should have really put in mind how to formulate this beforehand.
[ ] Jump straight into asking what's wrong with Makoto-san's powers.
[ ] Ease her into it by telling her about the Labyrinth.
[ ] Make Makoto-san do it. They just asked you to find her.