Valiullina getting the invite ahead of the other young Gamzatti debuts might be a sponsor/regional thing as the other girls are all from Moscow/St Petersburg but she is from Ufa (and interestingly so is Natalia Suprun who is dancing Nikiya during the same perfomance).
Definitely during her time at Vaganova she had a number of regional sponsors from Ufa that worked to promote her and fund things (like transport, extra costumes etc). I wouldn't be very surprised to find out that one of the sponsors for this festival (and maybe paying for Kimin Kim to come) is from Ufa/Republic of Bashkortostan - possibly connected to Komi Opera and Ballet because of Suprun who is principle there - and that they specifically requested Natalia and Sofia for this performance.
By the way even if this is the case I don't think it reflects poorly on Sofia or makes it less special for her to get to dance with Kimin Kim. Outside influences impact casting all the time and Sofia herself has almost certainly lost out on roles over the past year due to other dancers supporters/sponsors. She got support from these companies as a student because she was talented and hardworking and they (correctly) believed in her ability so wanted to give her the same opportunities the Moscow/St Petersburg girls get.
Thanks for sharing this, Anon! So interesting. Even if it's speculative, it's a reminder that there are so many behind-the-scenes influences to a dancers' career.