At 15 Dex, SH gets the most benefit out of her medium armour, since medium armour caps your dex bonus to AC at +2 - which she now has.
Out of curiosity, just as a feedback to the game thing, what was it that was making you think that dexterity had something to do with wearing heavy armour? Do you know where you picked up that idea, and was it something in game that led you to think so?
