I've noticed this strange bug and don't know what to do without killing her, since it's the only viable option that's left for me, but anyway here's the point:

I've ordered Uthgerd the Unbroken to follow me as normal. I've been to Shearpoint and Shimmermist cave with her with no problems, could give her orders, dismiss her, trade things with her, etc. with no problem. Killed some giants and mammoths, killed some random wild animals plus a thalmor squad with a prisoner. Now I've reached Dawnstar and when trying to give her orders, the follower menu won't show up, a notice shows up saying "your follower has left your service" and she attacks me for no good reason. Thing is she only attacks me when I try talking to her, if I just walk and ignore her she will follow me as usual and do nothing, but as soon as I try to activate her, bam. And cannot wait or sleep in-game because it says you cannot wait/sleep with enemies nearby. I have no bounty in any hold, and the only way to stop her is by killing her, sheating my weapons won't work. I've tried disabling and enabling her through console but no good. What can I do?

It seems like Uthgerd the Unbroken . . . is broken.

Bad jokes aside, does this problem occur only at Dawnstar or is it resulted from updating to 1.5?

Try loading a few previous saves just to see how far back the bad behavior goes.

kill her.

Sounds like you need to kill her.

Have you tried these console commands?
getrelationshiprank
setrelationshiprank <#>

0=acquaintance, 1=friend, 2=confidant, 3=ally, 4=lover, -1=rival, -2=foe, -3=enemy, -4=archnemesis. (All other values are unassigned ranks and will default to "acquaintance.")

From the Wiki

I'm really liking the Uthgerd mod from the Nexus. She fights intelligently, keeps out of the way, and specializes in light armor and archery. With this mod she's turned into one of the best followers in the game.

http://skyrim.nexusmods.com/downloads/file.php?id=6585