This is the 159th most frequent Japanese word.
かなり
"かなり" means "quite" or "fairly."
In this context, 'かなり' is used to describe the notable extent of her speed, enhancing the adjective 'fast.'
彼女はかなり早く走ることができます。
She can run quite fast.
The adverb 'かなり' modifies 'hot' in this sentence, suggesting that the heat is noticeable and beyond the ordinary.
今日はかなり暑いですね。
It is quite hot today.
Here, 'かなり' is an adverb meaning 'quite' or 'considerably,' indicating a significant but not extreme level of interest.