Hello Whistl. You're more than welcome to join in.
Chicken I can't remember if I cheered your DD yesterday, so have a belated standing ovation. I would consider starting with DD1. Rather than rewarding the results, ensure you are rewardi g the effort, then match it for DD2. I think one of the worst things that you could do at this stage is actually give DD2 the impression that you believe her future results won't be as great as DD1s, because in a teenage girl's mind you will have written her off already, so she may as well live up to expectations. However, we all know that your DD1s results are exceptional, so DD2 needs more realistic role models to inspire her. Does DD1 have more "normal" friends with a good smattering of 6,7 and 8s in their results? Use them as an inspiration, talk about their great prospects, any hurdles they had overcome and the exciting options open to them now.
We had a similar issue with DH's brothers. DH is a solid academic performer. His middle brother was labelled as the bright, quirky on (head boy, musical & straight As (before they had to invent a higher grade). Meanwhile his youngest brother was written off as being unlikely to achieve such glorious standards. He was chubby, ginger with a few OCD traits and as a consequence really suffered with self-esteem issues. Everyone did a double take when he not not got the A* equivalent of his older brother, but he won prizes for getting the top marks in the country. He went onto Cambridge, Durham & Oxford to name a few. I suppose what I'm trying to say is that your DD2 should be encouraged to exceed her own expectations, but I appreciate it's easy for me to say that without a concrete plan.