If your friend service is more than 3 months then as per "Delhi Shops and Establishments Act, 1954" section 30 (2) she has to serve one month notice or salary in lieu of the same.
If her service is less than 3 months than she has proof of her employment related documents like, offer letter, appointment letter, ESIC e-card, salary slip, or UAN of epfo than she may go for legal action. By filling written complaint against her employer in the labour department. In such case she has to proof following things:
*She was employed by the institute.
*Her date of joining.
*She was employed against salary.
*She resigned from the institute.
*She handed over the official stuff to her employer.
*She did not get payment.
24th July 2018 From India, Varanasi