So I gave this to Uthgerd the Unbroken as I am a mage.

She has used it fine.

I noticed that she had switched back to using the Dwarvern Longsword that she had before I gave her Dawnbreaker.

I thought that Dawnbreaker must have lost it's charge and so went to trade with her to take it and charge it up.

It's not in her inventory anymore.

Not sure where it's gone.

I haven't dismissed her so I don't really know what's happened here.

Any ideas?

I'm on XBox ONE.

is it possible she was disarmed? if so, it would likely have been dropped so she would revert to the next best item in her inventory

ah this would make sense.

I did see a Deathlord shout at her and Frea at one point in the Temple.

This may be what's happened.

Not sure if I can be asked going back to look for it.

Nice weapon but not something my Mage is going to miss.