There was only one girl in a hat on the cover and she was listed as 平山 which is why I assumed it was her. Which of the four are you looking for then?
From top left to bottom right sougouwiki lists them as:
篠田あゆみ
平山こずえ
高岡すみれ
二葉恵
They don't seem to be 100% sure of the last one but the family names of all 4 match the names given on the cover.
Unfortunately I'm on vacation and my hotel wifi isn't fast enough to actually download the movie, so your pictures and the cover of the movie are all I can go by.