Why has she not even opened my message its been 2 days!? Is she playing the waiting game?

So ive been talking to this girl for almost a week now, never met her before until sunday, i took her out on a spontanious road trip to the beach, and it went as perfectly as it could have gone, i never made a move until i hugged her when i dropped her home,

Literally we have loads in common and she told me she really enjoyed herself as well, she thinks im a funny guy really confident she was into me,

Then on monday at 11am i replied within the subject of our conversation and shes been online throughout the past 2 days but has decided to simply not even open my message and or reply, why? Its not as if shes been offline for48 hours, shes still online,

Is she playing the waiting game,? Its literally my pet hate,

What else could it be she still messages me at work and occasionally at the gym

Help.