Flagging something real quick - hopefully it's helpful
From my inventory, when I try to use pet items (Fishy Bits, Pumpkin Pet Biscuits, etc), clicking 'Use' gives me an empty 'Choose an item to transform' screen, with nothing to select:
Kim's identified that this is because the pets are on display!
Quick note: If you used an Orb of Ordering (available with MOA) on your display case, your pets will remember the order they were in on your display case, even after you take them off, feed them, and put them back.
Now go feed your pets!
From my inventory, when I try to use pet items (Fishy Bits, Pumpkin Pet Biscuits, etc), clicking 'Use' gives me an empty 'Choose an item to transform' screen, with nothing to select:
Like this
Kim's identified that this is because the pets are on display!
1. Take the pet off display
2. Use pet item, and the non-displayed pet should be available for you to choose
Quick note: If you used an Orb of Ordering (available with MOA) on your display case, your pets will remember the order they were in on your display case, even after you take them off, feed them, and put them back.
Now go feed your pets!
Just a heads up for people following this from home, I rebuilt this system so it is now possible to target items in the display case when using pet items 
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