I don't think she'll just be a cameo given that she was shown in the trailer. Every main leads and main supporting…
I think she has a deep relationship with her agency since they started with only her at first and she got a lot of advertisement deals with the agency.
Are you guys sure that Go Yoon Jung will appear in season 2? At this point I think she'll be doing another cameo in s2. I am not expecting anything anymore, I'll just watch and be surprised if she shows up.