A friend has recently found out that her bookkeeper has ommited the GST from my friends invoices when?

invoicing clients on behalf of my friend for the past two years. The invoices have shown the GST broken down and the cost of the service however the two figures have not been totaled & the clients have been paying for the cost of the service only not the GST. As her business turns over $100k p/a she is registered for GST. My friend has potentially missed out on around $9000.00 from clients. My friend has paid GST on the money that she has received however now that this has come to light she wants to invoice her clients for the rest of the money that she is owed. She has mentioned to her clients the blunder & they have told her that they will not be paying as it was her bookkeepers mistake.
Has my friend got a legal right to pursue this money we just want to get an idea on where she stands before we see a solicitor.

Thanks for the answers.
My friend has a cleaning contract at a motel after expenses & wages to her staff last year personally grossed $31,000. so this is a huge sum of money for her to have lost. Basically it means that she worked for nearly a third of a year with no pay it looks as though she will be wearing it on the chin unfortunatly.
The invoices were set out as in the second answer eg

service $1000.00
GST $100.00

Then there was no total at the bottom so the client has only paid the $1000.00 instead of $1100.00
We are going to work out the exact amount that she is still owed and invoice the client & leave it up to their own goodwill to either pay or ignore the invoice.

What a pity it was allowed to happen for as long as 2 years. I'd need to see exactly how the invoice and the breakdown to total price was set out to answer this. The total consideration for a taxable supply is deemed to be GST inclusive if someone is registered for GST, even if the tax invoice doesn't show GST charged on it. But if, as you say, an example tax invoice would say:
"Service $1000
GST $100"
... without saying "Total price $1100" you'd expect the customer and the bookkeeper to realise that $1100 should be paid. Or perhaps the customer is in the right for assuming that $1000 is the total price which is inclusive of GST, and assuming that the invoice just has the wrong amount of GST written on it (i.e. $100 instead of $90.90).

I'd take it on the chin and review and revise all my BAS's with the help of a real accountant if I were your friend. It would not be very good public relations to reinvoice all the clients and make them have to revise all their accounting records and BAS's.

Edit -
That's a good idea, actually. It should have been pretty obvious to the customer anyway. If any customers have still not paid the extra GST amount by the end of a certain time period, your friend should revise her BAS's to reduce her net amount of GST payable for the last 2 years.

That is, if she declared that she collected $100 GST on $1000 sales, she needs to revise the GST collected amount to $90.90. Except of course for the invoices she'll collect the GST on now - they will become total sales of $1100 with GST collected $100 - for which she'll only revise the total sales on the BAS, not the GST collected.
It will be tricky. She'll probably need a decent accountant/tax agent to sort out the BAS revisions.
Good luck to your friend.

I have had clients in a similar position with the end result usually being they have been left out of pocket. The problem is do you chase the back money owed ($9000 less your legal costs and if you lose you need to pay their legals as well) and risk losing the client and therefore future income or do you take it on the chin and move on? The bookkeeper can't be sued if she was an employee as anything she does falls back on the employer. if she was a contract bookkeeper there may be some recourse but your solicitor would need to advise on that one. Is your friends business that of selling goods or providing services? Did you know it is possible for your friend to restructure her business quite easily and legally and cheaply so that GST no longer applied, no matter what her turnover is.

Edit -

If your friend has only the one client I would be cautious for fear of alienating them and losing your only source of income. Otherwise listen to Miss Schlonky her words are words of wisdom.