Could there be an underlyin' reason for my sister's frequent, impromptu cryin', please, guys?

Lately, my kid sister, (whom, for the record's twenty-six), has been breakin' down in floods of tears, completely out of the blue, on SEVERAL occasions, (and, more often than not, when she's asked WHY she's cryin', she ain't got the faintest bloody idea why she's in tears- she reckons it just happens every now and again, and that furthermore, there don't even have to be a reason for it!) Could there be the underlyin' cause of this, please, and if so, what? Much obliged in advance, guys! Peace and love! Be lucky! :)