Maybe I didn't explain it clearly. Every item in a girl inventory is a line of text over a light blue rectangle. Let's change the color of equipped items' rectangle to a different color (green, for example).
I understand what you are saying and I have something like that planned for when I redo the inventory.
If an item is selected from either left or right, any girl with that item is highlighted in green on the opposite list,
If a girl is selected from either left or right, any item that she has that is in the opposite side will be highlighted.
Other things I have planned for the inventory screen include:
Adding a building filter so, for example, you can choose only girls in the arena to give armor and weapons.
Adding a "Vault" and "Store Room" to supplement the "Player" when the Player can actually use items like the girls can.
One question though unique girls born as daughters, is that coded yet? or no?
No it is not.