Company that fired my sister because she asked for offer letter

My Sister joined a company on 30th july 2025 (wednesday).she attended walk in interview on tuesday for research analyst and they selected and asked her to join on 30th july .She started on 30th july.they asked her to submit 10th certificate stating that they will give that to her when she is reliving from the office .on 31 st july she asked her offer letter to Team lead she said she will get offer letter based on performance.so in doubt she asked HR.She was not able to contact HR directly since she don't have access to bio metric  so said Team lead that she wants to talk to HR regarding Offer letter.The HR told that she will get the offer letter on 1 month..today(1 august 2025) that company have fired my sister  and then gave her certificate by stating below points.

1. That they don't liked her performance.it is very slow(its been only 2 days since she joined and there is no orientation happened).
2. She discussed about offer letter to employer(She just asked when she will receive the offer letter)
3. She discussed her salary with employer(they didnot give offer letter.they said they will give 10k so she had a doubt how much inhand she will get so she asked team lead not any other employer).

And Some rules i find very unsual.that are

1. They should not talk to other department employer(they never introduced her to all the employers or any orientation help.
2. Lunch break is only 20 minutes.
3. Once they entered office they have to hand over all thier phonce to teamlead in case of family emergency they have contact only team.

verbally they did not mentioned  they should not speak about our salary to other but still i checked with only Team lead .Ther is no contract n aggrement they have given as a proof but they collected my sister's certificate and delayed offer letter.My sister went again to collect the other xerorx she had given and as a proof she atarted recorder in her phone.some how they found and they asked her to delete it and after deleting they around 2 to 4 people were blackmiled and cornered her.after deleting also she took my sister's mobile and checked everything in her phone.What i can do for this scenario