Even a regular employee who does “mundane” work is mandated in mishna-halacha to shorten his/her davening and curtail his/her bentching to avoid “stealing” time from the employer, kal v’chomer when the employee is in kli kodesh – teaching Jewish or secular subjects (which is also a mitzvah) to multiple “employers”/students.
However, if the recess is so short that she is unable to get to the teacher’s room (which I am a bit skeptical about but accept at face value), then I assume the recess is way too short for the students too, and this ought to be raised with the school’s menahel/ess.