Do this...
Enter into your console with the tilde key " ~ " then type " Player.moveto 1a697 " this should instantly move you to her location in whatever state she may be in. If she's dead, which it sounds like she is, you may spawn on her body. If this is the case just enter the console command " resurrect 1 " while targeting her. If however you either don't get teleported to her or her body happens to of disappeared then simply run this command " Placeatme 1a697 " in which she'll spawn on you, give that a shot while standing in Jorrvask (Or whatever the Companions' hall is called). Apparently doing any of this will have issues with quest givers attached to the NPC such as Skjorn and Vilkas but it's worth a shot, aside from that there'd be one last try you can do...
I'm assuming she died during the "Silver Hand" part as she tends to take a moment to actually spawn, not sure which part you're on but I'll give you the IDs for each main part of the Companions quest chain, all you have to do is enter the stage ID in the proper location.
Command is " Setstage <Quest ID> <Stage #> " don't use the brackets, just enter the numbers and use a space between the ID and the Stage #. Look below for a full listing of the Companions' quest chain ID, you can also just complete the part of the quest you were on and see if that skips you ahead or not.
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As listed above, just select the quest portion you're on and then visit the link to which if you scroll down on that page you'll see the stage # on the left of the Excel spread sheet.
All of the ID information can be found at this link for any of the quests in the game.
http://www.uesp.net/wiki/Skyrim:Quests
Companions' Quest list.
http://www.uesp.net/wiki/Skyrim:Companions#Main_Quests
Taking Up Arms, Quest ID: C00
http://www.uesp.net/wiki/Skyrim:Take_Up_Arms#Find_the_Companions
Proving Honor, Quest ID: C01
http://www.uesp.net/wiki/Skyrim:Proving_Honor
The Silver Hand, Quest ID: C03 (Dont ask me what happened to C02 I have no idea)
http://www.uesp.net/wiki/Skyrim:The_Silver_Hand
Blood's Honor, Quest ID: C04
http://www.uesp.net/wiki/Skyrim:Blood's_Honor
Purity of Revenge, Quest ID: C05
http://www.uesp.net/wiki/Skyrim:Purity_of_Revenge
Glory of the Dead, Quest ID: C06
http://www.uesp.net/wiki/Skyrim:Glory_of_the_Dead
All source information is from
http://www.uesp.net, as well as being linked here from a reply to a post of mine from NikolaTesla (
http://skyrimforum.com/members/nikolatesla.1264/ )
EDIT: Also, if you're on an XBOX or such then this won't be much use to you.