Carolina Kostner didn't get a Grand Prix assignment because she isn't ranked high in the World Standings. Unless you are a "host country pick", you have to have a ranking (I think in the top 40, but I could be wrong on that)to be eligible for a Grand Prix assignment. Rankings are based on results for the last three years, and Carolina has missed those competitions. Juniors who move up to Seniors also are eligible for Grand Prix assignments based on their ranking as a Junior.
Peng, Zhang, Yu and Liu all have rankings in the World Standings, even though with different partners. So they qualify to be picked for a Grand Prix assignment.
Peng, Zhang, Yu and Liu all have rankings in the World Standings, even though with different partners. So they qualify to be picked for a Grand Prix assignment.