。
She couldn't get used to New England winters.
Literal
She [topic-は] New-England [genitive-の] winter [to-に] adapt [the act-こと] [subject-が] couldn't-do.
馴染む ('get used to, become familiar with, adapt to') is the verb of choice for slowly acclimatising to a new environment, person, or lifestyle. It carries a softer, more organic connotation than 慣れる ('to become accustomed') — 馴染む suggests blending in, settling in comfortably, while 慣れる is more about repetition wearing in. The pattern ことができる/ことができない nominalises the verb (馴染むこと, 'the act of adapting') and predicates it with できる ('be possible'); the negative gives 'unable to do.' New England winters are famously cold and protracted by US standards, but to a Japanese speaker the contrast may feel especially sharp depending on which part of Japan she's from.