The client paid half of their invoice. A credit shows up in the exact amount she still owes me. I am unable to even find the invoice I made for her.

Hi there,

First thing to do is to find the invoice. You should go to profit and loss and see if you can find invoice this way. If not, go to audit log, and find the void/deleted transactions. If your invoice has been deleted, you will create a new invoice and apply the payment to the invoice.

Thanks

Prachi