Seeking a book published probably in ‘40’s about girls at an international boarding school. Two sisters have problems adjusting, one wants to be like French girl Mimi who has black hair and wears red. Both girls eventually adjust with youngest who is a tomboy having a boyfriend who gives her Marron glaces. There is a plot involving skiing. This book belonged to my aunt and I probably read it in the mid-70’s and it was old even then. I think there was a character named Berthe or Bertha.