Are employement bonds legal, Harassment at work. Work location Delhi/Goa

Posting on behalf of my sister My sister is working in the hospitality industry. She graduated from college last year and got employed via College placements. They mentioned that she would be a trainee and made her sign a bond of 4 year (2 years as a trainee and 2 years as an employee with a penalty amount of 7.5 lakhs). She is being paid a stipend instead of a salary, she doesn't receive a pay slip. Are trainees governed and protected by the same laws that an employee is entitled to? It's training disguised as employment. They make her work 68 to 72 hours instead of 48 hours per week without overtime. There are days when proper breaks aren't provided. (During times like Christmas) She was forced to work for 15 days without an off. 12 hour shifts were a minimum, she has competed 14/15 hour shifts as well. There have been days where breaks longer than 15 minutes on 12 hour shifts were denied, the frequencies of such instances have increased recently. She was promised multiple sessions with leading industry specialists and factory visits. But the schedule is rarely updated. Only 4 sessions were conducted in a year, No factory visits. 2 HR sessions and 1 POSH session were also conducted. She has also has harassment and unprofessional language at the workplace. She's raised 2 POSH complaints. She received a voice message from her manager at 3AM where threats were made to physically harm her outside the kitchen, he later deleted the messages. (Please note that she did not encounter physical abuse but threats were made) The verbal abuser has argued / fought with her after a POSH complaint (Can this be considered as retaliation) The use of degrading/unprofessional language in the office is common in the presence of female employees, please note that this wasn't directed towards my sister. The manager/higher-ups were made aware of this several times but was dismissed as work stress. There have been instances where she was forced to travel alone in Delhi without a security escort at 10:30PM several times. This was when her official shift ended at 7PM but was forced to work till 9/10:00 PM. She did speak to the security team, was informed that cabs would be available after 11PM, this wasn't a viable option as she was exhausted as she was working from 10AM. There was another instance where her colleague was denied a cab when her official shift ended at 11PM as her residence was too far. She was informed by HR to move closer to the work location. She was denied a night time cab in the meantime when she was shifting to a nearby location. These are strong allegations, Who shares the burden of proof? And type of proof is accepted/valid? What is the eligibility criteria for a class action lawsuit? Is this enough to file a counter suit for the emotional distress/damage that she has faced? Her work location is Delhi/Goa, she is in Bengaluru now. She came home as the harassment was too much