So my friends are on a server I created, just a small forge one, then one of them named darthjynx, demated her TARDIS and then tried to remat but It didn't do anything.

She tried disconnecting and reconnecting, restarting her game and restarting the server but none of them work!  She is still stuck in there right now!!!!! Please help us! 

Go to the world save files, I remember there's a config for all the TARDISes (I can't be sure 'cause I'm on my phone). Turn "In flight" to false

 I looked but I didn't see the config file

Ask for your friend to try make another config folder as the same as the server's one, i had this same problem too but i deleted my old config folder on .minecraft and then it worked very well, i hope i've helped.

 The server doesn't have a config file

The worst is now she was on the beta tester server and well... she demated, and can't remat.

But its the on beta tester server so I don't have access the config files!

we have been waiting for a mod on the server but no luck,

It happend last night.

NVM

Admin got it and gave me command

 I can't thank you enough Sub!!

Issue resolved.

Locked.