we had an urgent referral for our DD3 recently to cardiology (still took a good 2 weeks lol). I think an Urgent Referral is given when a child is presenting with symptoms (ie your daughter collapsing). in our case it was our daughter having unexplained seizures.

just a heads up: cardiology is a seriously busy department. there is a high likelyhood of the wait being longer than you want it to. I would write down any of the worries or concerns that you have now so that you have them on hand to discuss with whoever is going to be seeing her.