I found no information on whether Sabine is a relative of Malte or whether she knows about him.
A map overview of Germany based on phone book entries lists the name Hossenfelder 34 times.
It seems the name originates from the state of Hessen (where Sabine is from). Nearly all other entries are from urban areas, so I think some Hossenfelder's moved there in the past. So there is very possibly a connection, the other question is how close they were.