Can I help my friend get this apartment? Should I?

This is in Germany, so laws you know about might not apply. Anything people-related could help.

My sister is moving out of her apartment. A friend looked at the place and would really like to move in. She’s between jobs right now, but set to start self-employment in December (which is when the rental agreement would begin). She’s sure to make enough money for rent in her line of work.

The landlord rejected her after one phone call. She has an obviously Turkish name, which he asked her about. He also asked whether she has a German passport (she does). He cited her unemployment as the reason.

Discriminating due to ethnicity is completely illegal, specifically for renting agreements. What would you do? I feel sad for her and I’d like to help if I can.