Can you use Star Crossed before Sona readies 4 runes?

My opponent played Sona, Harmonious and her ability that readies 4 runes has gone on the chain. Before that trigger resolves, I want to respond with Star Crossed. If Star Crossed later bounces Sona back to hand, is her rune-readying still a trigger I can react to, and does the Sona player still ready 4 runes?