She's been acting squirrely lately, always changing her mind suddenly.

squirrely 是由名词 squirrel（松鼠）加上后缀 -ly 构成的形容词。松鼠以行为快速多变著称，因此这个词引申为"古怪的、反复无常的"意思，形容人行为难以预测或不可靠。