General aviation instructor reported an aircraft loss of control when a student applied improper rudder input during a stall recovery. The instructor took over the flight controls and recovered the aircraft.

Narrative

I was acting as flight instructor on a training flight with a newer student introducing recovery from power on stalls. Before the student's first attempt I demonstrated one and emphasized the use of rudder for roll control at high angles of attack. When the student performed the stall; the right wing dropped to about 20 degrees during the recovery. At this point I prompted her to use rudder to roll back to wings level. The student then applied full right rudder into the bank which immediately resulted in a strong rolling motion. Despite overpowering the student and adding left rudder as soon as the roll began; the bank angle exceeded 90 degrees. There were no further issues recovering from the incipient spin using the PARE method; and according to ADS-B data; recovery was completed at about 1400-1500 AGL. I was caught off guard in this situation as I did not expect the student to interpret my instructions in such a way as to add rudder in the direction of the existing bank. I now realize I need to be more clear in my instructions by specifying which rudder to use in this situation; particularly with newer students.