Can't find Black Lilly!

This may sound really dumb, but I can't find Black Lilly, though I found here originally and found this item behind her

[spoiler]
Dexterity Tome
[/spoiler]

I thought she was found in one of the entrances by the Thieves' Guild, but I can't find here anywhere, am I looking in the wrong place? I've been inside all the entrances on the Thieves' Guild Street. I've completed all Narlan's quests and the Oberon Estate quest, if that makes any difference. Thanks!