Footsteps were heard, edging louder and louder as they approached my bedroom door. "Son", my mother complained, "It's been three weeks since you've started using this (insert online tutor) Brainly, and you're grades have not improved." Tired and ready to be concise to keep this dreadful and often demeaning lecture with my mother short, "I'm doing my best."
"You're doing your best?" she laughed and exclaimed in a brusque as she walked out of the room.
Lots of people refer to cold as a personality like ruthless or mean so mint is just another way of saying something like her life was icy cold or she gave me the cold shoulder.