My sister took her granddaughter to Highlander Horses out by Front Royal a few years ago and had a great time! It was just the two of them with a guide. Other places to look into are Fort Valley Ranch (also out by Front Royal - just west of there), Secret Passage, and maybe JBit Ranch.
^This is good to know! I want to bring my DD out for a nice ride fairly soon. I just need to save up a little and we will be making arrangements. I've heard nothing but praise for your place from other COTHers!