She follows the rest of the class out, only remembering her things on sheer autopilot. Several classmates ask what that was about.

"I wanted people to pay attention to me."

They stare at her. She  immediately launches into an unrelated running commentary about her weekend plans. She's talking louder than necessary and basically only making it to the lunch room because that's where the crowd is headed.. 

She has a packed lunch so she can squeeze into a crowded table and insert herself into the conversation. The consumption of lunch is going to be slow. and she keeps trying to talk with her mouth full.

They're not all looking at her and it burns. There's barely room for anything else in her head. She shouldn't scream, but maybe if she screams loud enough they'll pay attention and it will stop hurting and she'll be able to think.

A kid finishes lunch and puts on a pair of noise cancelling headphones and closes his eyes.

her last nerve  S N A P S. All she can think about is the kid brazenly ignoring her. If they're going to ignore her she'll make them all pay attention.

She screams in the kid's face and before he can react grabs a bottle of hot sauce and squeezes it as hard as she can manage directly in his face.

(fortunately for both parties in this interaction the hot sauce was only mild hot sauce and there was no permanent damage done)

The floodgates thus opened she starts grabbing every object on the table within reach and hurling it into the crowd.

After a minute the football coach manages to get to her and start carrying her off to the office, but not before the table is thoroughly trashed. 

She screams at the top of her lungs all the way down the hall. This hurts of course but the pain is nothing beside the pain of being ignored. (Everyone in the hallway is looking at her but they could be paying more attention to her, right?)

The vice-principal scolds her. The principal scolds her. The secretary gets her mom on the phone and her mom scolds her.

"You don't understand, they were ignoring me. I had to make them stop."

(some tiny part of her brain knows she's not really making any sense, but it's drowned out)

Eventually they sit her down in a side room to wait to be picked up and lock the door.

She screams at them to come back in. She bangs on the door until her knuckles bleed but it's sold enough would that she cannot (yet) break it.
After a little while she gives up. Obviously they've all forgotten she exists. Probably everyone has forgotten she exists. Probably nobody would notice or care if she was dead.

After a little while longer Meghan's mom comes in to find her sitting on the floor, with bloody knuckles, staring into space. Anger instantly melts into concern and she kneels down to hug her daughter.

"Meghan, sweetie, what's wrong? What's going on?"

It takes her a little while to react. Her mom is here? Her mom knows she exists?

"You have to tell them I exist. You have to tell them to pay attention to me."

"Meghan...."

"Please, you have to. I need it. Please. "

"Come on sweetie. Let's go. Actually I think we should go to urgent care. To look at your hands if nothing else. Did you hit your head too?"

She collects Meghan's bags which were delivered to the office by the janitor and are only slightly coated in food residue from the trashed table.

"No. But I can tell them I did if that will get them to pay attention to me."

"...It's their job to pay attention to you so they can help you. But you have to tell them what's actually wrong okay?"

"Well I need them to pay attention to me. They're not paying enough attention to me. That's what's wrong."

By now they've made it out to the car. They climb into the back seat and Meghan's mom fusses over the seatbelts and tells the car to drive to the nearest clinic.

"...Why are you harping on this? This isn't like you. Are you sure you didn't hit your head?"

"Yes I'm sure. Only my hands. Because they locked me in and ignored me." pause for half a beat as she actually manages to consider the rest of the question, briefly , "I don't know why. I just...I need it so bad it hurts."

Shoulder squeeze. "I'm here. I'm not going to ignore you."

"It's not enough though..." She's glancing out the window "They'e not paying attention to me..."

"Well, you don't have to pay attention to them either do you? I'm right here." More shouldersqueeze. 

"But I know they're there. I know they're not paying attention to me." She's trying to refocus on her mom though. Fuck those guys. They're missing out anyway.

Eventually the car pulls up to to the dropoff area in front of the clinic and then goes off to the parkcade. They go inside and talk to the nurse on duty.

The nurse listens to the explanation of what happened (delivered via Meghan's rambling attempt at an explanation punctuated by frequent 'Are you listening to me?' and asks if Meghan can bend and straighten the fingers (she can) and asks about other symptoms and family history.

"I'm going to send this to information the doctor and see what he thinks. Go sit down please and we'll be with you shortly.

(this universe has reasonably funded if not extravagantly funded healthcare systems and staffs properly because sometimes people just get stolen by evil pocket dimensions in the middle of their shift, it won't be an unreasonably long wait)