Theseus had a lot on his plate. He was in no way interested in partying it up with any of the Greeks for such an occasion. Dionysus had sent him an invitation he felt just to be an ass and rub it in his face. There was still a power the God had over him from the night terrors. It was something that Theseus was none too proud of, but not able to easily dismiss. He still went through hours of sleep deprivation, and it showed under his eyes.
In fact when the woman (whom he had no idea was his grandmother) walked into him. He couldn't even remember if he'd ever met her. His father wasn't exactly too keen on family reunions (and neither was he). "I'm fine," Theseus said in a bit of a haze. He knew she was immortal and his hackles instantly raised.