Hi,
Pronouns don't lie. They are instinctive, they require no pre thought. They are 100% reliable. We use them millions of times. Baby's, pre speech use them reaching out clasping their hands indicating mine. We don't mix them up. If i asked you to recall a past event you attended or a situation, would you pause to think, was i alone or with someone. You would know without thinking. Crimes have been solved by noting what pronoun is used.
"WE" shows unity, not just that there are more than one person.
Example:
"I was at work to get the to cash box put safely away when two men screamed at me, cursing, telling me to stand still. They placed a plastic bag over my head and said for me to not talk. WE went into the back room where they took the money box."
The word "WE" indicates unity and cooperation. With such a vicious robbery, where suffocation via plastic bag was in play, there should be no use of the word "we" in his language AFTER the robbers enter the scene.
IMO, Grandma let slip by using, "WE"
MOO