Yep...you're wrong 🙂   The death itself wouldn't preclude claiming the exemption.

The issue is that the death (& her SSN) has been reported to SSA & IRS.  Dead folks SSN's are often snagged for identity theft/fraud - you'll need to paper file the return.   

Don't forget Form ???? explaining why you can't efile (Lacerte give a nice diagnostic to remind me of that)