Remus Lupin: 

After Sirius got put into Azkaban, Lupin adopted Sarah because Dumbledore didn't know about Sarah, therefore Lupin didn't know where Harry had been brought. (That's good for Sarah.) I imagined that as Sarah became more aware about her life story, she and Lupin would argue a lot about what they think is best for her. 

Sirius Black:

I put that Sarah spent a lot of time with Sirius before the night of the attack. When Sirius got thrown in jail, she kept telling herself Sirius was innocent.

Draco Malfoy:

I also wrote in a girl name Denna Malfoy (Draco's twin sister) and the girls went to Beauxbatons together and were best friends. Denna used to invite Sarah over during holidays so Draco got to see her a lot. Draco starts to get a little crush on her while she's still at Beauxbatons.

Denna Malfoy:

Sarah's best friend at Beauxbatons. She ended up moving to Hogwarts the same year as Sarah to improve her English. She starts feeling left out because Sarah starts leaving Denna to convince the Gryffindors she's related to Harry.