It sounds like it's possible that the save broke, but before you do anything, try looking at the guide on the wiki under each character's profile. The wiki is linked to on this page :)
I already looked at the wiki and tried for days to get the event to trigger, nothing worked. I fixed it by using a RenPy safe file editor and advanced her relationship level by one. Now the level 28 event triggers just like stated in the wiki :) I will update if it causes further complications down the line.