Ah, that's jealousy for you and it's also very flattering. Easy solution. Tell her that you bought whatever you bought in another shop. And make it impossible for her to copy you. Buy accessories in junk shops, make them yourself or buy them in supermarkets/accessory shops and add your own touch. (Depending on what you wear, a metallic rose, a handknitted scarf with just one unusual thread knitted into it, jewellery from your granny, dye your T-shirts and mix the colours, sew different buttons on your tops, change the shoelaces, etc.)
It's the biggest compliment of all if someone tries to copy you. Frustrating though.