Someone Else's Secret by Julia Spiro

2009. Lindsey and Georgie have high hopes for their summer on Martha’s Vineyard. In the wake of the recession, ambitious college graduate Lindsey accepts a job as a nanny for an influential family who may help her land a position in Boston’s exclusive art world. Georgie, the eldest child in that family, is nearly fifteen and eager to find herself, dreaming of independence and yearning for first love.