Gamer Luna does exist, but not in the way most would think.
Luna was too shy to go back out into society, so she spent most of her time in her room. Celestia offered her some rehabilitation, but since this would take a long time, she gave her a couple of games to keep her entertained. While it took a few weeks to figure out, Luna grew to love this strange technology…almost too much. She eventually began skipping her rehabilitation sessions, not wanting to stop playing in order to do so.
Eventually, she practically barricades her room, only allowing servant ponies to enter with food. Soon enough, she begins neglecting her own hygiene, and even begins to put on some weight.
Tired of being trying to be more patient (after all that nasty Nightmare Moon business), Celestia goes full drill sargent and whips Luna right back into shape.
And that’s why Luna was late to the wedding; she’d just finished that day’s workout and had to hop in the shower before getting dressed and attending the wedding.