Frustration with a studio?

so i dance at a dance studio in michigan. our studio is putting on a xmas show on sunday and for this one dance, we had to get fleeces from old navy. this past weekend my mom sister and i were at old navy, saw them , and bought them for bout $9. the studio wanted us to pay $18 for the same fleeces. well the instructor for this dance found out my mom and us purchased them ourselves and while she was waiting in the lobby for us to finish rehersal, the instructor went up to her, and in front of everyone in the studio, yelled at my mom because she "didnt have the right to go out and buy them" she went on and on about this in front of everyone in the studio. when we were done our mom told my sister and i. now in this show, we are performing the nutcracker. i am the nutcracker. i dont think it is right for the instructor to yell at my mom who has been with this same studio for 17 years (since my sister and i were 3). i was wondering if i can get some feedback on what i should do about this situation. my opinion is to tell the instructors on thursday (my next cl) that i will not be doin the nutcracker this weekend and i think my mom deserves an apology for the way she yelled at my mom. thank you for your suggestions