She can very well claim for the days she worked. They have no right to hold salary for a single day.
Proof of Employment
1. Have they given an offer letter before she joined? If not, what proof or evidence does she have as an employee of that company? Kindly ask her to see whether she has an ID card, offer letter, salary slip for the last two months, bank statement if her salary was credited to her account, etc., to claim the rest of the salary.
Company Obligations
2. The company cannot deny paying any dues to particular employees, and they cannot stop any employee from leaving their organization without a strong reason or without mentioning any clear clause on the notice period/resignation, etc., in the appointment letter. The company should also mention the Notice Period Buyout clause in the appointment letter to help the people who cannot serve the notice mentioned in the appointment letter.
Legal Implications
3. In your case, the company did not provide an appointment letter, and they did not discuss the notice period, etc. It is illegal if they hold her salary.
Action Steps
4. Ask her to talk to the HR of that company and demand the same. If they are not accepting, let them know that you are going to take legal action and see the reaction of HR. If it is unfavorable, you can always take legal action with the support of an advocate. Don't think about what is the point in taking legal action for 25 days' salary because you can claim much more than what they were supposed to pay as they denied and delayed in settling her dues.
Regards,
M. Kannan