Q is a supposition. There is a tendency for some modern scholars to assume that there is a common written source for Matthew, Mark, & Luke…
Now, this is just my own idea, but I have mentioned it before in discussions on this subject, so for what it is worth:
The traditional teaching for generations has been that the first Gospel was Matthew in Hebrew/Aramaic, & that our present Matthew, Mark, & Luke all used Matthew (Aramaic) as a source…Well, wouldn’t that be what “Q” is supposed to be?
I guess I just have to wonder at the motives of teachers/scholars in trying to raise up an idea that confuses & upsets people’s faith in the Gospel accounts, when there is a perfectly good, & perfectly orthodox, explanation for what they are talking about…
My point is, that you really don’t need to worry about this so-called “Q”, because believers have always known that there were oral & written sources that went into the writing of the Scriptures…Only, it seems like, these days, there are a lot of people with a need to prove that those of us who take the Bible seriously are somehow missing out on their “brilliant new discoveries”.
And, yes, it’s true, Mary was a source who was right there. The apostles & other disciples of Jesus were sources that were right there. There were all kinds of sources, including the original written documents that were used…There were oral sources–As someone whose grandfather was the last in a long line of folks whose main source of history was the old Oral Tradition from the Appalachians, I can tell you, that the Oral Tradition was word for word. It was extremely reliable.
It’s just a modern label. Don’t let it confuse you!