Can anyone help pls ?

my niece travelled to Cancun at the beginning of Jan and has a return ticket to UK at the end of April. She is a UK passport holder.
when she arrived she was allowed to stay in Mexico for a maximum of 180 days, but i understand rules changed after her arrival and its now up to the discretion of immigration officials how long one can say and this will be written on FMM form on entry. This is pretty unclear on hers and she is panicking that she might be deported or thrown in jail if she exceeds whatever is supposed to have been written on the FMM. Does anyone have any ideas as to what is the best way to get this clarified & sorted ? Ideally she would prefer to stay as per her original ticket

Many thanks