Why didn't Gamora collect the Orb for the Collector?

In Guardians of the Galaxy, Ronan sends Gamora to intercept Peter Quill on his way to the Broker.

But, some time earlier, Gamora had accepted the same mission from the Collector. (This occurs in the MCU canon "Guardians Of The Galaxy Prequel Infinite Comic.")

When she accepted that mission, she even said, "I do not trust you, Tivan, but I trust Ronan even less. I will obtain the Orb. And you will keep it safe." Why did Gamora apparently disregard her mission from the Collector, wait around for a while, and then only go after the Orb once Ronan sent her to intercept Quill?

What is going on here?