@smarson  "when I file the 1041 and report the sale proceeds, do I need to indicate anywhere that I'm reporting proceeds from her SSN?  Something like "as reported on XXX-XX-XXXX" so they can match the 1099-S to the 1041?"

IRS survives by convincing most people that there are enough of them to keep a close eye on all of us.  The fact is that there are fewer than 75,000 of them, and most aren't auditors.  And there are more than 150 million of us.  At least, that's how many stimulus payments they plan on sending out, and those don't even go to people making more than $100K/$200K.  So do you really think they are going to be looking at any explanation you try to make of why an SSN was used when an EIN should have been? 

They aren't even going to look at the return of a 2019 decedent whose survivors sold stock after he died, and forgot to tell the broker that the account now belonged to an estate.  (There's another discussion about that right now on this forum, with a preparer wanting to go through some paperwork gymnastics to balance a 1099-B to a final 1040.)  Just remember, you and 2000 other Americans share 1 employee at IRS, who might be the one who makes the coffee in the morning.  Look beyond the smoke and mirrors, and just keep the work both you and they must do, down to the required minimum.