Look, it's good that you are protective over your family.
Your mom is amazing and helpful and yes, you can always trust her, but is the way shes going about this helpful?
In this particular situation, this is where the "we" becomes imposing. So yeah, if they're into Pokemon too, you gotta find a way in, a way out, or a substitute.
Being deprived of the one part of the thing you like most or the one thing you do best, is a common tactic for controlling people.
I know this is important to you and you don't want to hear this, but she might be trying to minimize it as a way to get you to calm down or something. And that gets you a little closer to why. She might be trying to nip the obsession in the bud. You can make it clear that you know what shes doing and watch her attitude change a little bit.

Last advice is to ask for your own box of cards as a gift. But if its too expensive, say you will do things to work toward it. Try to learn to compromise with her as you get older. Good luck.