Because they want to have an all Russian final. They won't do this by putting Trusova and Kostornaia against each other as this is counterproductive, but if they'll smart they'll put one of them against her as well as someone else who is very good but not necessarily at the top of the list. I could see Trusova and Tarusina vs. You at one and Kostornaia and Gubanova(if she competes) at the other, or maybe Shcherbakova for the second spot if they decide to have her go against Trusova/Kostornaia. They want You to finish second at the highest, best case scenario 3rd or lower.
The point is that they will never put them both against her at the same assignment.
Also, i really don't think its such a big deal. In worst case, she will be like the #6 entry at the final, like Kihira was this year lol. Its not like they care that much, really, their main focus will be giving each of their girls the best chances to get into the final by doing crazy substitutions.
I've seen people all over twitter talking about how she's being over dramatic about this change of hers but she's excited, she was with the same coach at the same place since she was 6, she's discovering new things. Of course it's exciting for her 

