How many customers are required to issue a 1099 to caterers?  Like, it's not on the list of services offered by wedding planners.  You are spinning your wheels with a transcript request -- especially since it may take forever now that IRS has just started accepting them again. 

Follow the suggestions of @qbteachmt and @sjrcpa , and familiarize yourself with what an IRS auditor would do if the decedent were still alive and an unhappy customer (perhaps with food poisoning) turned her in.  How much of the income was paid by check, and how much in cash?  Even bank deposits might not yield a good picture of gross receipts, and of course expenses may show grocery shopping that was strictly personal.  

I would probably do a "lifestyle" audit and figure out how much she had to net to support the house where she lived, the car she drove, and her other personal expenses.  Her survivors should be able to give you more useful information, than her bank.