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Sharing this info with your mother isnt a bad idea. If she gets to know that you are hiding things from her, you may loose her trust. And since you are a considerate and smart girl, you should tell her, not just for the trust & bonding but also for future advice too, after all she knows what best for you.
Takecare.

I can tell from your post that you are actually pretty close to your mother. Most daughters would not usually take into consideration their mother's feelings for this matter. Unless your mother has extremely conservative views on tampons (i.e. if you use tampons, you will lose your virginity..etc) then maybe you should hold off on telling her until you're a little older. If the subject does arise in a conversation between you two and you feel comfortable enough at the moment. Then go ahead and share with her. She would probably feel really good knowing that you trusted her enough to talk about such sensitive matters. Also, it's a sign of maturity to be able to handle tampons and menstrual related topics on your own, but also be able to share with your mother. good luck!