I think this is her first time using silver aura. Silver Aura basically not just Ragna only thing since Ragna didn't have that in the first place he acquired it by struggling. I think to get the Silver Aura, one must struggle fighting dragons a lot and pretty much the princess struggled on this one. It may not comparable to Ragna's future self struggle but considering that princess has the innate ability to control silverware and to see auras, she pretty much has an upstart to use Silver Aura than Ragna's future self (adding also that she saw how Ragna use it with her ability to see Auras) so she didn't have to struggle that much compared to Ragna. Still not comparable to Ragna's Silver Aura though.