Bastian, are you using the Wizards and Wands rule set?
https://www.gmbinder.com/share/-LsXE64qLDdLgBczM2kA
Coincidentally I ran across this last week, and then I saw your post!
I like withcdoctor's ideas of getting her character involved in Hogwart's itself. If time travel is too complicated, maybe just things like:
- the annual scavenger hunt for 1st and 2nd years
- receiving detention due to her nemesis and meeting the house goblins in the kitchens while doing chores
- discovering clues to a mini-Chamber of Secrets, without all the death and dark magic!
I would probably consider setting each adventure a few months after the last one, throughout the school year, so one for September to Halloween; one leading into Xmas vacation; one for January to Spring Break and then maybe a summer vacation one that takes place in Muggle-world.
Sounds like fun, enjoy!