Free-Winter's Kill the Bandit Leader and other similar missions will also interfere with Shahvee's quest triggering.
...and I have done (probably) all the other favor quests ('cept Ahtar's), so no doubt killed Shahvee's somewhere along the way.
I was looking through console commands and the Creation Kit, and noticed that Shavee's quest-giving line seems to be linked to her mood. When she's sad, the PC should be able to get the prompt line, "Your people have bad luck?" but she's always in happy mood when I greet her. I tried various "setav mood (tried various numbers from 0-9)", "modav mood (#'s)" and "forceav mood (#'s)" - the system replies that the console and script cannot be used to "modav" or "forceav" mood, but the command to "setav mood" is accepted, but doesn't have any effect on her state that I can see - my PC still gets the line about "Are you always this happy?". I have also tried "addtopic favor204getfavortopic" in combination with various "set av mood" #'s (I'm not sure what # corresponds with sadness, so I keep running through them all) and also without messing with her mood: all to no avail. And as stated, have also tried "resetquest" and various "setobjectivecompleted" commands - but all have been fruitless.
I'm thinking that if I can figure out how to use the console to force her to at least
offer the quest, then the same mechanics may help with Ahtar and/or Ghorbash (has anyone ever gotten the quest to get Ghorbash's ancestral axe?).
And, once the NPC at least gives the quest - even though the quest may stall out later (like arriving at Uttering Hills to "Kill the Bandit Leader" but because Linwe is already dead, you have a quest marker floating over nothing) - you can at least (on PC) use the console to advance and complete the quest (sorry console gamers - I know you couldn't probably care less) at that point - which at least gets you the item, follower, or whatever result accompanies the completion of the quest. Whew. Wordy.