Kate's investigations is a route in Adventure High.
During it, Kate is trying to deduce if Brktnye (Brittany) is legit or not.
You're free to help her out, if you so please.
Or you could just ignore her and carry on doing other things.
Really, the choice is yours.
Do note that this is just a general outline for the route. It is not a walkthrough.
Rescue Girl's Plea
After meeting with Rescue Girl in the dungeon twice, she shows up in the Town Square, asking the Protagonist to help her find out more about Brittany, who she considers to be... unnatural.
If the Protagonist refuses, another scene plays out in which Kate has confronted Brittany and the two of them agree to meet up to discuss things further.
If the Protagonist agrees, the Protagonist can speak to Brittany who says she'll happily speak to Kate.