work it out for yourself

答案：mysteriously．

根据题干When asked what she meant，she said--（神秘），"Work it out for yourself"．可知句意为：当问她是什么意思时，她故弄玄虚地说："你自己想吧．"．句子中said是个动词，应该用副词修饰．mysteriously，副词，神秘地．故填：mysteriously．