@vza004
The speech bubble reads "私の教え子ぐうぜんねぇ" (watashi no oshiego guuzen nee). Oshiego = pupil, guuzen = coincidence. I read it as "A pupil of mine, what a coincidence hey?" which I English-ified into "What a coincidence! I used to be her teacher!" to make it clear the dorm mother on desk duty...