Pete, since I posted my question, I looked at the funeral scene several times based on what SC posted about it. Here's what I
saw.

There's a closeup of the line of limos at the funeral as Dons exit them. Once that finishes, at the distant end of the limo line, you'll see a women in black exit a limo. She's wearing a headdress (just like Mama wears in the shot of seated Corleones). Yes, in both scenes it's Mama. In that distant shot, you can make out Tom escorting her and right behind them is Fredo.