That's weird. It worked for me. Maybe check if you have anything else left to do and come back to it later?
let me recap the trigger scenes for videl .the first scene of Videl was accessed when I got the sphere for the kame and found Videl at the shower, the 2nd after encountering pan(also found Videl at the shower), the 4rt was after the body switch and found Videl at the living room, the 5th was finding pans picture, finally the 6th was buying the shades/sunglasses.
Do you have the scene after the body switch? There was a scene with Videl in the shower after giving her the picture but before buying the glasses. I think you might've missed it and I don't know if there is any way of going back to watch it. The scene was Videl giving a blowjob to the body-switched Pan.
I honestly don't remember. I played the game till I didn't see anything else to do, so I installed the prequel, and it installed itself on top of this one. So I can't play this one while I have that one. And I'm waiting for the update before installing it again. So yeah... You might stumble upon it unknowingly, but I haven't got a clue.
Also, there's a problem with both games, which is that after unlocking a bunch of scenes, saving and closing the game, when you came back, all the previous scenes that you unlocked will be locked again, even after loading your savefile. So if you save and close the game, when you come back, the old scenes that you have already unlocked before, and cannot access again, are now locked forever, unless you start a new game. And even if you do, this can still happen to you again. So yeah. A bit of a problem there.