She needs to try and get the visa sorted as priority as I've already mentioned. But she can make her claims at the Employment Tribunal in the meantime. This can be done on-line and it doesn't cost anything. It is also possible for her to name you as her representative (if you/she want) so that you can handle things on her behalf if she has to leave the country.
It's entirely right to list her grievances, but make this an appeal against dismissal - because that is what they have done, dismissed her.
She has three months from the date of dismissal in which to make her claim in the Employment Tribunal.
OK, the claims so far from what you have told us are:
Unfair dismissal
Failure to allow accompaniment to hearing
Unlawful deduction from wages
Wrongful dismissal/Breach of contract (no notice or pay in lieu of notice)
Failure to provide holiday entitlement
Failure to provide written statement of particulars
Failure to provide payslips
(If I think of any more, I'll edit to add them)
So the appeal is against the unfair/wrongful dismissal - but also listing the other grievances.
Download the ACAS Code of Practice that you can find here:
http://www.acas.org.uk/index.aspx?articleid=2179 which outlines how the dismissal should have been handled, where they've not complied, list it in the appeal letter. The Code of Practice is a statutory instrument which the Employment Tribunal take into account when deciding whether a dismissal was fair or not.
The directgov site gives loads of info on other employment rights, as does the ACAS site.