I would suggest you to get her physical health checked up to confirm that she is not having any general health issues. If there is any, please get it resolved through your family physician or under her / his guidance. If you find the condition unchanged even after that, please consult a psychologist and get guided on further action. If the 'crying for no reason' spell continues, she may have to see a psychiatrist. However, I feel that checking her physical health is the immediate need.
Next Steps
Please consult your family physician right away and a psychologist, if required, thereafter.