Yooo I got it
Check the attached image
Long story short: Basically, re-do the quest, but before going in the bank, DON'T wear the fox hat. She'll tell you to wear it, but fight her instead and it'll drop.
Long story/detailed:
It's going to be a bit more complicated. You want to do this in the bank, while no one is on your left side. Otherwise you'll trigger the police event making it a lot more annoying. Just leave and come back when no one's to that side. Once it's clear, she'll give the dialog to wear a mask, but you whack her instead xD
You'll notice if you keep going too far to the right she'll keep spamming the "Hey, hide your face" dialog. So this is where you bait her to the far left and you can get her there. Now, she may or may not drop the mask. She dropped all the other things except that, for me.
Have sex with her, then take her to any free jail cells if she doesn't give you a mask right away. Easier said than done though; avoid triggering the police or it'll take longer to complete. Once she's there, you go inside and see if she'll drop the mask. If she doesn't, no worries, just leave and re-enter. Another tip would be to have her strip the clothes you already have. For me, it seems to drop the unobtained items a lot quicker if you do this.
Hope this helps. I have every item (being the collectionist that I am) aside from this 6k glasses item. I'll get that soon though.