Linette is MC's dead mother.... So zero chance it's her...
It's clear this character doesn't want to be recognised so my guess is it's Cathy.... or perhaps even Mona...
Couldn't think of anyone else that might need to be disguised like that at a party.... Not an outfit to party..
Only reason i can think of it's not one of them, is if it's somebody we will meet in next episode, so either somebody that is connected to the inheritance, that wants to see MC before that meeting, or somebody that is keeping an eye on some other character close to MC for whatever reason....
(think of Maya's mother looking into her behavior; is she the "Priscilla" that Burke called after the talk with Maya)
But no doubt we will get more info about her later.... DPC will have put her there like that for a reason....