How to make a homemade menstrual cup

I really want one, but my mom is too stupid too learn anything about them and she must think I'm a little kid because she won't let me use one. She's so quick and stubborn. I REALLY want one. Please help. thank you.

Order one in secret or go to boots if you live in the uk and buy one, use it and she will never know, make sure you use pads and tampons so she doesn't get suspicious. X