Go to Class, she can still make it to the end of the lesson.

She rushes to class in a hurry, after all, she is already late. She remembers that Byleth had told her that she would be expelled if she didnt come to class. She hopes that was all a dream, but just to be sure, its better to be late than to not show up. That's what she tells herself anyway.

As she opens the door to the classroom, Byleth spots her and notices that she is, despite what she was told, wearing clothes. Not only that, but she is late to class as well. She would have to play this cool though. No one knew that her and Rhea had conspired on this plot, so she couldnt just call her out right here. "Welcome to class Bernadetta. You're late. I'm going to have to ask you to stay after. I need to talk about your punishment."

"I... understand professor" she says as she slinks into her seat.

The class continues for the rest of the lesson and the students file out. Soon it is only Bernadetta and Byleth left in the classroom.

"Bernadetta. Do you not remember what I told you? About clothing? About missing class? This is serious. Your place at this academy is in serious jeopardy right now. I'm going to have to beg Rhea to not expel you."

"That was real?! NO! Please!"

"I don't know what to do here Bernie. You can start by removing that uniform. I'm not sure where you got it, but the longer you wear it, the more trouble you are in."

"B-but!"

"No buts. Off! Now! I don't want to lose you as a student! Please just listen to me!"

Bernadetta shyly removes the uniform and folds it neatly on the floor. "Please! I can't go back to my father! I need this academy! I couldn't accept that what you told me was true. I was sure it was a horrible nightmare. You have to help!" she gets down on her hands and knees and begs.

(Art Credit: https://www.pixiv.net/en/users/58172120 )

"I'll see what I can do for you. I really hope you don't have to leave. Ill do my best to convince Rhea. You have my word. Just wait here for me. I understand you are embarrassed so you can hide in here for now. I will be back to tell you what she said."

Byleth would love to have Bernie be exposed to more people, but she has to regroup for now. She is willing to give the shy archer a few moments of privacy. After all, whatever comes next would be much more fun. She now has an excuse to step things up a little bit.

She goes to meet with Rhea. Rhea of course doesn't actually intend to expel Bernadetta, but she is willing to help come up with something extra embarrassing to tease the poor girl with.