In most hives I seem to spot her right away, but sometimes, for various reasons a queen may be difficult to locate. I had one hive that was like that, just yesterday. I used my usual technique to find her, I carefully examined each frame in turn, checking first one side then the other and looking closely where the comb meets the frame. I went from one frame to the next, then back again. I did not find her. So I escalated my search to the next level; I returned early this morning to repeat my search process. Bingo, there she was on the first side of the second comb I examined.