The lady, while attractive, does look like she's headed to a cocktail party rather than work. Though it's not really my place to tell women not to dress up or "appear attractive."

Contrast it with her actual profile picture on the site, both are flattering but completely different in what they communicate.

I think there would have been a significantly smaller chance of rejection had they gone for the profile picture on the engineer's toptal page, not the "professionally" done headshot.