This is a phrase that I came across in the Macmillan Proficiency Testbuilder:
'Can't you just tell me?' Lisa pleaded, but Pete jutted his chin and said he was only obeying the rules. Lisa stretched her eyes at him. She had been brought up to be wary of anyone who believed in rules.
I have never encountered the phrase "to stretch your eyes at someone" (legs, arms - yes, but eyes?). My first guess was that she gawked or stared at him. Then I realised she probably put the tips of her fingers to her lower lids and literally stretched them down to make fun of the man's attitude. Do I understand correctly? This seems like really odd behaviour, though, considering Pete is her teacher.