As owner occupied property lenders will view this much more favourably than investment. ( max 90% lvr for investment) If you can prove her income has been consistent over past years (tax returns etc ) and her business doesn't have debt then they should be able to factor her income into servicing.
Btw, when the loan gets assessed, they will assess it at a much higher rate (ie 300 basis points above advertised ) to ensure mortgage stress is avoided so if a bank knocks back the loan amount even if you can make repayments by your calcs this might be why. If you haven't done so already call up your bank or broker and have a discussion and get the ball rolling. Some banks issue aip/ conditional approval straight up while others issue it after assessing your application. Since you've found a property don't waste time getting the aip.
Just ask the lender or broker what's required and they can give you a breakdown.
