If you had already gotten the event once, you should be able to play it again to unlock the still that are behind them. For example with Mia's Main Event 2 if you choose jeans then you miss out the still of her taking her tank top off, but you can replay it and choose the other option and still unlock it.
Of course if you had missed them unfortunately you will have to replay and try to get them again. I would advise saving when any of them get to a new stage and then run through everything they have as progress on Event and hangouts is retained across all saves.