Another thing to find out is if anyone in the office is a union member. Only one person needs to be for everyone to be able to be represented by a union official.
Not true. At all.
Rumblebee, sorry for being late on the case... I've been through a very similar process. I was there for 8 months and was offered 2 months pay to go quietly. I refused (because there was no case to answer) and I was booted out anyway with zero pay. I appealed, the appeal was a joke and it failed. I tried to go to a tribunal on the basis that I was being racially discriminated against, but was told that racial discrimination against a white person had never succeeded in that region, and wouldn't do in my case, so we dropped it.
Had I posted in time I would have recommended she refuse the meeting - she is entitled to more time to prepare, and time to arrange for a union rep or personal rep to attend.
Unfortunately with her only there for 5 months, if they wanted to get rid of her, the need do nothing more than pay her notice period. Given that they clearly want her out, it suggests they are not entirely clued-up on employment law - why not just pay her one months notice??
There is absolutely no up-side to this situation - sorry for not pulling the punches. If she goes, she's out of a job. If she stays, she either works in an unsuitable environment or is sacked later (minus the 2 months pay). If she stays and they falsify evidence against her, make her job impossible and effectively orchestrate her downfall (however blatantly) there is absolutely nothing that she can do about it.
The *ONLY* get out of jail free card is if she can prove sexual, racial or religious discrimination - this will qualify her to waver the 1 yr qualifying period for a tribunal. If she gets to a tribunal, she likely wipe the floor with them. IF.....
So she has a Hobson's choice: quit and take two months pay, or stay and hope that they say something sexist to her.
You are already chasing ACAS which is good, and it's never to late to join a union. There is little they can do here, and probably wouldn't be willing to anyway (until she has been a member for a while), but they might at least confirm my advice.
Sorry I couldn't be more positive...