She was going to protect Clark

"You knew what she was up to all along!" 

Clark was furious; he didn't want Emma to become a mercenary, to tread a path similar to his own.

"I knew, and I approve." 

Frank offered no defense, his nonchalance strangely calming Clark's anger somewhat.

"What do you think is best for her?"

 "Becoming a mercenary will bring too many dangers!"

 Clark remained unconvinced.

"I've secretly checked her physical condition; it's good, and she can integrate the simulation seed, which means she's suitable. Do you think you can protect her for a lifetime? How can a grown man be so hesitant at a time like this, without any backbone?" 

Frank's scolding made Clark realize fully that he couldn't always be by Emma's side; she had to face many things on her own!

Perhaps this was indeed a better choice!

"I'm actually glad to have this opportunity." Emma spoke softly.