형 means the same as 선배 in this case. It is not rare for a female junior to call a male senior as 형 instead of 선배 or 오빠 in Korean colleges.

I have seen some dramas, Did We Really Love (in which Bae Yong Joon is a main actor), a female junior call a male senior by 형

haha have you seen "Good Doctors"? Yea it should be 오빠