Due to SH's now 15 DEX, she went from a -1 DEX mod to a +2. This means that when she wears medium armor, she now adds a +2 to her AC instead of subtracting a -1, and results in her having 3 more total AC. I'm thinking this is where your confusion came in. She didnt gain access to other armors, she just got much better at wearing the armor she already could.
She is a tank now, plain and simple. 19 AC + Mirror Image + Armor of Faith + Heals. She just needs a taunt and then she can just stay there while the rest of the party does the DPSing.
