I wouldn't waste a lot of time on what shoulda coulda woulda.... get a wage & income statement for the periods with missing information and file the returns. The IRS will calculate P&I and she can pay or setup a payment plan.  

I estimate the preparation fees and take a 50% retainer, and require signed engagement letters first. 

I administer a rewards program for these clients and give them up to 1000 "frequent delinquent filers points" with each accepted return.