Every GM handles SINless stuff a bit differently in my experience, so realistically, what could she know to expect if she didn't use it and just said she didn't have one?
I imagine classic SR. SINless means you can't do any legal stuff, can't use a credstick, can't go anywhere legal, can't buy food. All activity will have to be shadow activity. I figure if Eunbyeol said she'd didn't have one, they'd take her down to the station, confiscate everything because none of it is licensed, and either register her officially, or deport her, depending on their investigations. Illegal immigrant so to speak.
Deportation might be a quick way to get closer to the main plot. XD
Things were not looking good. She had no doubt what would happen if she didn't use her SIN, but she also knew that the one she'd bought wasn't anywhere near good enough for anywhere that was actually going to check it. Still... What choice did she have? She was going to have to show it. She held out her comm, sliding her fake SIN to the top. She braced to throw herself back into a fight if need be. She might just be able to get out the door if she was lucky.