You clearly have no experience of this whatsoever if this is the advice. All this will do is mark the OPs card, and won't get her a penny any faster.
And in no universe, under any law, does five days constitute a reasonable deadline in law, no matter how justified the ire is. 28 days is normal, 21 at a push..
OP, I understand the frustration, but you need to do this correctly - even that may not be good for future relationships with your employer, but that's a decision for you to take when and if it comes to that.
The correct procedure is to raise a grievance laying out what you are owed, when it should have been paid, and what solution you would like. That should hopefully resolve the problem. I'd suggest that your requested solution is the payment of what is owed, within xx days (21 or 28 are normal), and an undertaking that future payments will be paid in a timely manner. I can't see it going beyond that - but if you don't get a resolution you'd need to appeal.
Unless you have done all that, the tribunal would blame you for not taking the proper steps - and your employer can really drag it all out for a lengthy period for you to get nothing more than what you are owed.
Start looking for another job if this is your only option left.
Of course you can alternatively take your employer to the small claims court. You will need to write a letter before action, explaining your claim and giving them a reasonable period to pay - again 28 or at best 21 days...
... see previous advice about looking for a new job now.
I totally understand it's frustrating. And no way should an employer let things get to this stage. But you still need to do things the right way. Threats about tribunals in five days are not only laughably not the right way, but simply make things worse. They may not be the best employer. They may have idiotic systems that aren't fit for purpose. But none of that means you want to burn your bridges with someone who is still your employer..