Yes, there might be. There are numerous fanfiction websites out there where fans create all kinds of crossovers. You could start by checking popular fanfic platforms like Archive of Our Own or FanFiction.net. Just search for 'Harriet Potter Red Ridding Hood' and see what pops up.
One possible plot could be that Harriet Potter is on a mission in a magical forest that also happens to be the setting of the Red Riding Hood story. She meets Red Riding Hood and realizes that there's a dark magic at work causing the wolf to be so menacing. Together, they team up. Harriet uses her knowledge of spells and potions, while Red Riding Hood uses her knowledge of the forest to defeat the source of the dark magic.
Yes, there are likely some interesting ones. Fanfics often combine different fictional universes in creative ways. Some might explore how Harriet Potter's magic world intersects with Red Riding Hood's fairy - tale realm. Maybe Harriet could help Red Riding Hood deal with the big bad wolf using her spells, or they could go on an adventure together in a new, merged world.
One of the morals is about the importance of heeding warnings. Little Red Riding Hood's mother warns her about staying on the path, but she strays from it. This shows that if we don't listen to the advice of those more experienced, like our parents, we can get into trouble. Also, it can be seen as a cautionary tale about the wolf - representing evil or danger - being able to disguise itself as something harmless, teaching us to be more discerning.
You can try some popular fanfic websites like Archive of Our Own (AO3). It has a vast collection of fanfics from various fandoms, and there's a good chance you'll find Harriet Potter and Red Riding Hood fanfics there.
The story is about a little girl in a red hood. She goes to visit her sick grandmother in the forest. Along the way, she meets a wolf. The wolf tricks her and gets to the grandmother's house first. Then it pretends to be the grandmother. When Little Red Riding Hood arrives, she notices something strange but it's almost too late. Finally, a hunter comes and saves them.
It's highly unlikely to be popular. 'Futa' related content is not only inappropriate but also goes against the general ethics and norms of most fanfic readers and writers. The Harry Potter fandom, in particular, is very large and diverse, but the vast majority would shy away from such inappropriate takes on the story.