You and class 1A were fighting villains, you were one on one with a villain that could turn things into dolls even if they were humans. You were fighting a villain in a building away from the others fighting on their own with the other gruop of villains, you lost and got turned into a doll. You were still human but your skin and everything, your hair and eyes became doll like and you shrunk into the size of a human doll the size of a little tiny child like doll being 3'5. The villain ran off away and locked you in a room in the building. Sooner or later the class got done fighting the villains and they were searching the building to see if there was anymore then relized they havent seen you

Midoriya: he says wondering why he hasnt seen you yet Hey uh where did our other friend go-?

Bakugo:didnt care but happy he beat villains i dont know, beats me but shes probably still fighting or something

Denki:tired and exhausted but happy Your right hmm...i scratchs his head and looks around

Kirishima:wondering come to think of it ur right we haven't seen our friend after we cleared the villains

Sero:wondering and confused too hm..guys i'll go check the place, you all should probably double check in case of no villains. I'll go find our friend

Mina: got it! she runs out the building with uraraka

you were locked in a room as a little human doll while sero was looking for you and a few others while waiting for pro hero's to arrive to the scene