Hm. So I've been saving for weeks to get this Chibi Potion, and I just got it from the Millionaire Center. I gave my pet Glowstick a Kanis Potion, then the Chibi Potion. The Kanis Potion gave me the "Glowstick is now a Kanis" message, but the Chibi Potion.. didn't, and instead just directed me to my (now empty) inventory. I went and checked her profile and she's still a Common Kanis. It's not caching, it says she's still a Common Kanis as well.
So.. where did my potion go? I hope I don't need to buy another :/. [edit] Problem resolved.
I don't think you'll need to get another one. I believe you can equip a Chibi Potion to your Pet if I'm not mistaken. Just check your Pets Equipment. This happens a lot because those options are so close together xD
I don't know if Chibi is one of the potions that can be equipped as a weapon, but that's usually what's happened when someone's missing a potion. Have you checked her battle weapons?
If it's not there, and you've also checked your shop and vault just in case, you should fill in a ticket. Staff will find it.
You can also equip potions as a weapon. Go to pets and then go to edit battle weapons and see if it is there. Here is the link that should work. http://www.subeta.net/pet.php?act=battle&petid=577013