Invoicing regarding owner's part-payment to pay the invoice.

Hi, this is a rather convoluted query so I'll lay it out as best I can.

Problem:  The owner bought plant on a single invoice where the company paid 3 separate installments, and the owner paid the 4th installment out of her personal bank.  The invoice wasn't issued until all 4 installments were made.

To deal with the all four installments in the simplest way, I simply entered the invoice 4 times showing each installment value so I could match the payments.  I applied all of them to an Other Asset account with the intention of depreciating the plant purchase, so a Capital account.  Easy, for the company-paid 3 installments. 

However, the 4th installment, being the owner's own payment, is a problem (to me).  I need to:

1.  Close this invoice, and

2.  On closing, somehow show that the company owes the owner this invoice value without losing the Capital account value.

The only (incomplete) solution I've come up with is for the owner to temporarily deposit the money into the Owners Equity account, I pay the invoice by taking the money from Owners Equity, and them set up a purchase invoice where the company owes the owner and paying by the cheque account so the owner receives the money back. But, while this would give the owner back her money (2nd amount) and close the invoice without hurting the capital account, it still won't show that the company owes the owner the 1st amount.  

I might have been thinking about this too long and am missing a very easy solution, but I just can't see it.

Many thanks.