Yeah, rat face is definitely not Rum since that's what the mangaka wants us to believe...Also, this celebrity woman appears often in the manga, now that could be just because Kogoro loves her and the mangaka wants to have that comedy around or it could be that she is one of the BO people. She is hidden in plain sight and the BO has never shied from recruiting people in the public eye as proven by Vermouth and Kir. Also, she is casually hanging around Kogoro probably because Gin has always been suspicious of him and Gin is high ranking so I assume he told the boss and people above him (namely Rum) about the issue.
I'm just speculating but it makes sense
