This newer translations is definitely more understandable, I'm glad I reread it.
Fuutarou caught Ichika in 2 lies and I think the guilt is finally catching up with her. Now, not only does Ichika think she "lost" but she might think Fuutarou hates her, so she is purposely using her insider information to not see him. Hence, the "evil" smile she has is actually regret and pain, to the point of her stomach hurting. At least that is my interpretation.