Is there any difference between 姨丈 and 姨夫？
amongst "姨丈", "姨夫", "姨父" or "姨爹"; "姨丈" is the most common one.

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000150395

imo, your teacher is . . . :(