The creepy part was the manipulative way she got Sam to invite her. May be a pet peeve of mine, but I know a few people like that and they don't ask for anything but look pathetic and sad until you offer it.
I wouldn't know, perhaps she is used to be left out the fun activities. At least she's actively socializing now. Perhaps I'm just an enabler, I do give people several chances as (almost) always see the good in people.
As for hanging out with younger people, or doing 'kids' stuff. I remember thinking back when I was a teen that I should act my age, no longer watching cartoons and stuff, but then I thought screw that, I should do what I like doing and not live a certain way to appear grown up. What's next, no more gaming? After all as a kid you can't wait to grow up, as grown-up however you'd wish to be a kid again. Also I found out in high school/college that the girls actually like the kids channel, though this may be some kind of maternal instinct.
But I remember having the uneasy realization Marigold was having, when I was trying out WoW for a couple months when it first came out. I was doing some quests with someone, which turned out to be a 9yo girl(or so she claimed). And that was just virtually following someone, which felt a bit creepy, though the dilemma was that if I didn't know that fact, it wouldn't have been a problem. So I suppose it society which makes us think it's either creepy or letting you're realize you're playing a 'kids' game, which by extension might turn it into virtual babysitting, which might feel too much like it being a job. But once you get over that it becomes less of deal, after all I shouldn't discriminate based on age, right?