Maryse is one twisted piece of work. After this, I’m even more convinced that Maryse is completely incapable of feeling any emotion for anyone else; including her own kids. Maryse was going to throw not only Jace under the bus, but as Luke pointed out she would be putting her own biological children under suspicion. And for what? To save her own ass maybe?
But I have to also admit, that for that to make sense, there should be something in it for Maryse. She really no logical advantage to gain by not allowing the inquisitor to judge Jace. But Maryse does, as Luke pointed out has a lot to lose if she doesn’t cooperate with The Clave.
In the end, this passage makes Maryse look good at all, and overall this passages makes little to no sense. I actually believe that this is another blunder on both Cassandra Clare and her editor’s part. This bit should have really been cut altogether from this book.