A, then C. It’s best to prevent further harm before you start treating the wounds.

D: BUZZ LIGHTYEAR!!!

@redweasel  
Liking the mute & shield-spell suggestions, but what’s stopping the unicorns from TK-binding the various potential ‘infectees’ at a safe distance?

“those are fake memories, rarity”
 
“but I like these fake memories!!”
 
rainbow dash cast no spell to take twilight’s memories. whatever “spell” it is is a gigantic megaspell whose radius almost reaches fluttershy’s cottage powerful enough to tear pieces out of your brain. casting a spell to reverse what rainbow did can either fail pitifully or worse, work
 
I say ‘B’ but only because of the off chance that the crazy is transmitted by touch, since tying her up would offer plenty of opportunity for transmission. a voice loss spell combined with twiligh-I mean rarity’s shield spell should do nicely.
 
but option ‘D’ staring at each other like a mexican standoff waiting for the next pony to flip out might be better.

I think B is good
 
 
JK. Do A or maybe C

B

I’m not sure of what’s going on here, but A sounds good.

…are we absolutely sure Shy didn’t ‘catch’ whatever jumped from Redheart to Dash (assuming the Nursie isn’t playing possum)? Better immobilize all three of ‘em before working out your next move. A, then B or C, assuming Amnesiac!Twi & Rarity can pool their resources & crack some books for a spell along either choice’s lines.

Going with A.

a, A! For the love of Celestia, A!  
heavy breathing

C

I don’t see how Rarity is going to do the latter two, so A.

I’m. Bored. B

My vote is C.