At this point I'm wondering if they have him bugged or not, since they took her as a hostage right after he talked to Tenji about how it's safer for her to keep her distance from them.
If she's going to be sticking around as a character, I hope the author gives her real character development, like the ability to doubt others and act/scheme, to set the stage for her being able to graduate from being Shiho's puppet (just my personal impression). At the current rate, she feels like a "bomb" herself, someone who Shiho could manipulate at a critical moment to screw over Shuuichi.