This was actually the plan that all of them came up, all those who had a major role in the battle. Eureka would deal with Chiaki but after doing so she needs to wait for her energy to return. The others will then confront the other enemies.
She watched from the back, Raven and the others are doing just fine while battling Silver. Though it is still visible that Silver is indeed a very formidable opponent. But Eureka knows, she also heard raven exchanging place with Hideyoshi, that those three would be able to handle Silver just fine. They didn't need her help.
They are still a bit strong because of the help of those guardians. They can even easily use magma despite little practice over it. To which Silver have difficulty in nullifying. And they have trained more than enough just for this day. Adding Hideyoshi's continues stopping of his teleport.
