My Mii keeps changing to the Mii from the 3DS

     Hello Nintendo, I remember the update when the 3DS can now have an ID network as well.
There was a question of what Mii to use, either from the Wii U or 3DS. Since it's been a while since I chose the Mii from the 3DS, I didn't knew it was going to change my Mii from the Wii U. And now I'm havin an issue to keep both systems to their own Miis. (My little sister owns the 3DS and I own the Wii U, so we want our own Miis seperated.)
Any best solutions to fix this problem?
So remember, my little sister's Mii is being duplicated to my Wii U's account. And I want to stop that!