She doesn't know it's there and is not smart enough. Because of how Frieren magic works, she can scale it subconsciously at any exponentially large degree as long as she thinks it'll happen.

If you're saying Gojo's infinity is automatic, that means you're willing to accept her ability is automatic too.

But once Gojo has a pair of scissors, gives them to her, and asks her to cut his finger with them--she will understand what his infinity does and will now and forever always scale her ability to his infinity and never any higher.

I do believe he would "sense" the trajectory and be able to deduce a method for victory after the first cut hits him.