I’ve heard of that from our urologist.  He said that sometimes even non CAH girls don’t sit on the toilet correctly.  They keep their knees together while sitting on the toilet and slump over with bad posture.  This causes the urine to flow into the vagina and gets trapped there momentarily because of the labia.  It’s particularly common if the girl is at all chubby like all toddlers and preteens (even if only in the labial area).  This condition he said was called vaginal voiding and could cause the urinary tract infections and the drippage you’re talking about.

He suggested to us that we teach our daughters to urinate with her legs slightly open (meaning knees apart) and back posture upright.  That way it doesn’t flow backward into her vagina.   It’s worth a try anyway, and then if it’s still a problem I’d get it checked.