Recently got Aranea as a follower, and at first she would not put on any robes I gave her. In one dungeon, I found a nice helm to give her, and she put it on without complaint - got out of the dungeon and noticed that while she was wearing the helm, she now seems to prefer to go around in her undies - no robe at all.

Is this some sort of a bug, and is there an easy way to resolve it? Will she ever decide to re-adopt the habit of wearing clothes, or am I destined to be followed by a powerful mage in her knickers?

if someone wears hooded robes and you give them a helmet, their robes will be unequiped. It is not a bug.

She's in her undies.

What's the problem exactly?

But I've given her two different robes that aren't hooded - she won't wear them.

If I could enchant her undies with some bonuses, no problem at all!

because the hood is linked with the robes it is equiped rather than a hoodless robe.

Followers won't wear gear unless it's 'better' than their standard togs..

Give her something with an armor rating and she should put it on.

She's not wearing a hood, she's wearing a helm - "Vokun" to be specific. That helm is not linked to a robe. She also has two (non-hooded) robes in her inventory, neither of which she'll wear.

They don't consider bonuses? Like magica regeneration bonus?

If that's so, that looks to me like something in need of correcting; that a character won't prefer wearing a robe with a bonus to wearing nothing at all looks like an oversight, and something that should be patched.

Nope - you could create enchanted robes that make her more powerful than Gandalf, Sauron and Saruman combined and she still wouldn't wear it.

Extremely unlikely, at this stage. On PC there are mods that enable followers gear to be specified.

^ Ah, here's where I think I might just go looking for such a mod. Thanks.

Maybe she's hinting around at something...

She's easily more than 200 years old.

... oh

200 Years for an Elven Mage means Aranea is in Her prime, Your should be a