From Day One

From day one of Kate's first year at college, her mother saw her as both 'green' and naive. If she had known how soon Kate would become involved with a boy met at a first-week mixer, Jean would have had her home those first few weekends instead of "getting used to being on her own."

初日
しょにち

初日から、彼女は間違っていた。
しょにち  から、 かのじょ  わ  まちが って いた。
From day one, she was wrong.

Denshi Jisho has

間違い
まちがい
1 : mistake, error, blunder
2 : accident, mishap, trouble
3 : improper conduct (e.g., between man and woman) ; indiscretion
common word ; noun

間違う
まちがう
to make a mistake, to be incorrect, to be mistaken
common word, Godan verb with う ending

Perapera browser plugin gave me

初日    しょにち    (n-adv,n-t) first or opening day; (P)
初日    はつひ    (n) New Year's Day sunrise
初    はつ    (adj-no,n-pref,n) first; new; (P)
初    うい    (adj-no,n-pref,n) first; new; (P)
初    うぶ    (adj-na,n,adj-no,n-pref) innocent; naive; unsophisticated; inexperienced; green; wet behind the ears; birth-
初    ぞめ    (suf) first doing of ... (ever, in one's life, in the new year, etc.)

Google translate gives

それは彼女の初めてだった。

for

It was her first time.

and

それは、家から離れて彼女の初めてだった。

for

It was her first time away from home. 

NOTE: also from Denshi Jisho web pages :

グループ１動詞
グループいちどうし
godan verb
noun
 
子音動詞
しいんどうし
consonantal verb (e.g. godan verb); consonant stem verb
noun

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