fierce intellect

Hello everyone. I would like to know what "fierce intellect" means in the following sentences:

I called out to Charlotte Fisher, whom we’d employed to look after Rosalind and also to serve as my secretary. The arrangement worked out well, as Rosalind attended the Oakfield school in Sunningdale, leaving Carlo, as Rosalind had taken to calling Charlotte, largely free during the day to assist me. When Rosalind returned from school, Carlo tended to her so I could finish my work and focus on Archie. Her no-nonsense Scottish demeanor and combined with her patience and humor to make her excellent in both roles, a far cry from the irritating Cuckoo, whom I couldn’t wait to let go.

- Marie Benedict, The Mystery of Mrs. Christie, Part One, Chapter Thirty-One

This is a mystery novel published in the United States in 2020. The story is mainly set at the present time in 1926, when Agatha Christie suddenly went missing for eleven days, but also goes back to the past time in the 1910's. In this scene, set in an early time in 1926, the narrator Agatha is calling her secretary Charlotte Fisher.

In this part, I am wondering what "fierce intellect" would mean.
Would it mean "savage" intellect? Or "extraordinary" intellect...?
It seems like an unusual combination, so I wonder what it means... 👁 Big Grin :D



I would very much appreciate your help. 👁 Smile :)

I'd read it as "extraordinary", with perhaps a hint of "applied".

Dear cidertree,

Thank you very much for the explanation.
So "fierce" here would mean "extraordinary," and "advanced"! (Is it right to understand that "applied" means "advanced"...? Or perhaps "practical"...? 👁 Big Grin :D
)

Then, perhaps "fierce" would have the following definition, meaning that she has a strong/intense intellectual ability.

fierce - WordReference.com Dictionary of English

3. vehement, intense, or strong: fierce competition

I sincerely appreciate your help. 👁 Smile :)