She's hardly a cougar. There's no way she's over 30. Even over 25 is a stretch.
Ignoring the comics, it looks like she was went to the doug dimension at a pretty young age. Paying attention to the comics and making assumptions about ages, she was Twilight's age in S1 maybe when she crossed over so she's like 2 or 3 years older than them?
The portal originally opened every 30 moons, right? Assuming that was true when she was banished and there wasn't a Starswirl spell going on (she knew about the portal, so I'd think she used it to get there). So she could have been banished either 2.5 years before EqG, 5 years before or 7.5 years before. I'm going with 5 only because of the portraits of her winning the Fall Formal crown 3 times prior. That leaves one year in middle school assuming she's a senior.
I still hold onto my headcanon that Twilight is a high schooler in doug because ponies reaching adulthood slightly faster.