Here's Janis Ian looking very short next to Celine Dion and several other ladies:
http://www.celinedion.us/images/event/2009/janis-ian-celine-dion_20090113cin010.
And even shorter next to some guy:
http://www.pmpnetwork.com/photos9/SingerJanisIan.jpg

And, though you didn't mention her, I've seen Iris Dement in concert three times and was surprised at how short she looked. Like the others, she has a powerful voice, and maybe that makes me expect them to be taller. But I think a lot of great singers are very short.