Hi – Info greatly appreciated, I’ve been out of HR for a while now

A friend has been pulled up for an error at work…she lost a shop key on the premises but found it again the next day…

She was suspended, then received a letter informing her of a hearing on Thursday. The letter also details an incident which happened a month ago, also issues which she has not been spoken to over and wasn’t even aware they were issues dated from the day before suspension back about 4 days over the previous week.

Is this allowed? Can the boss bring up issues that were never dealt with a month ago and have a go at her now?

She has never signed a contract nor viewed any form of disciplinary procedure documents belonging to the company.

Thanks for any advice, she’s beside herself.