I've got a feeling it's an intensifier for the statement, but I want to be certain about the grammatical stuff behind it, since I've only seen one mention of that in all of my materials and research
Not sure what the context of the sentence is, but it means "only". And I feel like it's a little stronger than if it were to use だけ.
見たことないものばかりだわ！ → (There are) Only things I've never seen before (here)!
Every thing here are what I've never seen before without exception!