Hi Molly
Much depends on how high the Loan to Value ratio was on the first purchase.
if she paid LMI them ,it may be very cost effective to grab a new loan on the old IP to 90 % lvr and use that as a deposit.
The cash she holds is often best reserved for later non deductible use ( ie PPOR, car, holidays etc) and can usually be parked in an Interest only Offset account if that works
ta
rolf