How to equip Serana? [duplicate]

Solution 1:

Serana is capable of wearing both light and heavy armor, but the armor must be an upgrade over her default gear for her to equip it. From her appearance, I'd guess that she is already equipped with the female version of the Royal Vampire Armor. She will also equip enchanted rings, amulets, circlets, and some weapons.

Solution 2:

I've found that can equip Serana with about any armor that you want (including custom armor in the Steam workshop). Usually it has to be a higher rating, but from the console you can removeallitems 0 to drop the vampire armor. Once that is done you could openactorcontainer 1 and put into the inventory whatever armor you want the follower to wear. I found a good example of Serana with custom armor (along with some other followers):

_{(source: virtualsecrets.com)}