I've noticed that your profile picture looks exactly like mines.. I don't know if it's a glitch but I am worried for obvious reasons. 

One very important part is making sure you can actually get the cup in your country. For me, I can only get three different kinds of reusable cups in the US. Lunette is one of them.

 Personally, my mom and I have a really open relationship, so I talk to her about every concer I have. She and I recently discussed the Diva Cup, so that's the one that I"m getting :) 

I'm going to shamelessly plug the thread I started a while back:  How did you decide upon which menstrual cup to use?  It seems a lot of teens favor Meluna, given their selection and sizing.  Next seems to be Lunette.  I use the Diva Cup, and that's been working well for me, but I'm 26 years old (our bodies seem to change a little bit in those 14 years ^_^).  Also, take the time to check other threads discussing menstrual cups (click the tag at the bottom of your question to find them) and always feel free to add your two cents.  The more input from everyone, the better! :)

 There are a ton of brands available. It all depends on where your cervix sits during your period. If you Google menstrual cups, you can find a ton of communities who can help you out with information regarding all of that. I would post links but I don't want to upset someone. Start with research first, especially research that includes all the cups and their dimensions.

As for your mom, arm yourself with links that discuss the pros of menstrual cups and the cons of tampoms and pads. There are videos on YouTube and other websites dedicated solely to informing women just how bad tampons and pads can be for their health. Sit her down and show her these things, then explain that while a cup is costly, it is a one-time payment and pays for itself after a few cycles and there will be less waste in the bathroom during your time of the month. Make sure to stress to her you are sure of this decision (and make sure you're ready because the learning curve can be easy or tough).

Good luck!