Guldeniz had 50% of perfect passing in the last match. It means Gala is in system half of the times she receives. There's no way you give up on that. The problem is the setter, who wastes all her good job at passing, making pointless her presence on court. The most comfortable player with the setting for Gala is always Kosheleva, simply because of her spiking reach; she can at least adjust and kill the ball some times. The others can't.
Güldeniz's seasonwide perfect passing is 32% and Ilkin 28%. On the other hand, Güldeniz has attacked with 30% whereas Ilkin's attacking was 40%. To Güldeniz's contribution at reception doesn't compensate her lack of offense. Maybe in a team with strong attacking MBs, such a sacrifice would make sense but everyone knows that GS's MBs are not that strong. Moreover, both main attackers of team are playing with high sets. That's why there is no need to get perfect passing. A team like GS that has very limited score contribution from its MBs can not afford to play with second libero on court for the sake of good reception. It makes sense for instance for Nilüfer Belediyesi, or THY but not for GS