Betty's name is on the "Well Wishes" card you find with one of the backpacks. I believe Glory's name is on there too.
Betty's also in the prequel novel, if I recall correctly.
I think the only major members of the traditional supporting characters who aren't acknowledged or referenced at all in the game are the Stacy's and Randy.
There's a backpack that has one of MJ's first articles with the school newspaper that quotes Flash, I believe.
One of the other backpacks is a pin for the "Spidey Squad," Spider-Man's fanclub, which I also imagine Flash is a part of.