Well, clearly there is a boy involved, who is doing the feeding. Then there is the 'gf', which stands for girlfriend. And of course, there is an implied narrator, who is the one whose girlfriend is being fed by the boy. It's possible there could be other characters in the background depending on the full context of the story, but these are the main ones we can assume from the title.
Yes, it's completely normal. Fanfic is a popular form of literature among many people, and your gf is no exception. It's just another way for her to engage with stories she loves.
Since I don't know the exact 'Sleepy Time Gal Story', it's hard to say. But likely there is the 'Sleepy Time Gal' herself. There might also be her family members like her parents or siblings if it's a family - centered story. Or if it's set in a school or work environment, there could be classmates, teachers or colleagues.
If she does it as a form of joking, try to find other ways for her to express her humor. Maybe suggest some funny group games or topics that don't involve teasing your friend. Explain to her that while you love her sense of humor, it should not be at the expense of your friend's feelings.
Well, it's a tricky situation. Start by sitting down with your girlfriend and having an open and honest conversation. Let her know that family is important to you and that her forcing your mom is not acceptable behavior. Listen to her side too, there might be some misunderstandings. Then, communicate with your mom as well. Assure her that you'll handle the situation. Try to organize some family - friendly activities where they can interact in a more positive way. If your girlfriend continues to force your mom, it might be time to consider whether this relationship is right for you in the long run as family harmony is crucial.