Complex sentence: She says Jocelyn was once a Shadowhunter and had done small things for her (such as painting a pack of tarot cards for her) and asked Madame Dorothea to keep a look on any gossip or news of Valentine.
Split into simpler sentences: She says Jocelyn was once a Shadowhunter and had done small favors for her (such as painting a pack of tarot cards for her). She had asked Madame Dorothea to listen for any gossip or news of Valentine.