Lydia equipped a mage robe and won't give it back!

I gave Lydia several items to carry, including a simple mage robe that had zero armor rating. She carried it around for a long time in her inventory, and then suddenly out of the blue she was wearing it! And now she won't give it back. When I try to take the robe is says it was her original armor. Why did she equip a robe with no armor rating when she was wearing the heavy steel armor before that? Is there any way I can get her to let it go?

Solution 1:

Give her an ordinary piece of fancy clothes she should un-equip the robe if not if you marry her you can buy them from her

Or you could just buy some other robes if you don't want to do that then get the thief skill were you can pickpocket equipped items and pickpocket it.