Yep, it's happened to me a few times with unreliable girls, but I usually find out when I confirm at 10am. It is one of the hazards of pre-booking an early appointment with a known unreliable. Amy & Emma were notoriously bad at this with their hangovers...I always had a plan B.
I guess they keep Delta on because when she does turn up, no doubt she gets lots of bookings and is a good earner.
Still, it's bad form of them to let you travel without telling you that she hadn't confirmed that morning. I would have stressed most strenuously that I was travelling a long distance and had been let down before and didn't want to be let down again, that way you may have got the truth of the situation and could have held off travelling until the girl had actually arrived in MK.
Still at least you know now...and you've let other punters know the lie of the land!