Restaurant Close No salary

If they are formally going insolvent, but they have been operating the payroll correctly beforehand, reporting figures and paying tax and NI to HMRC, then you might be able to get arrears of pay from the Redundancy Payments Service - part of the Insolvency Service - gov.uk/gov…nce
But if that requires a case number from insolvency practitioner handling the insolvency.
But from your comment "the owner is in no mood of paying Dec wages and holidays pending for this year" it isn't clear if the business is a limited company going into administration, or a sole trader going bankrupt, or just a continuing business that isn't inclined to pay what it owes.
If the business is continuing then small claims court or employment tribunal might be another approach, but as others have said, it's probably best to talk to Citizen's Advice first.

Contact citizen advice

In theory this can be claimed via an employment tribunal but they will need to wait 3 months and a day before they can claim (I think it is). Speak to Citizen's advice, ACAS but crucially, try and keep tabs on the employer. If you think there is a chance they might disappear, try and note where and to whom the business is registered (it won't necessarily be the restaurant itself).

Acas ?

If your friend bough legal cover with home insurance, she could give them a ring for advice.

How long have they worked there?

Is there any contract of employment etc?