The difference I see here between what you describe and what Ruby is doing, is that you are continuing hobbies and interests from your own childhood, rather than just doing childish things. If Ruby had said "when I was a child I used to play pretend cafe for my family every weekend, we were reminiscing and I decided to do it again today for nostalgia and giggles", that would be far less weird. (Still concerning taken with the wider picture of Ruby's behaviors but I'm just looking at it on it's own for a moment.)
Lots of people go back to things from their childhood when they seek comfort, like watching your favorite kids' movie, making yourself a silly meal, reading a book you loved, etc. That's totally normal. If all you were doing were these things, while not engaging in any new or more adult hobbies and interests, that would maybe point to some issues. Ruby goes a step beyond that, in that she engages in these childish things which seem to not even be from her actual childhood.
Yeah, and it's not just that all her waking life is playing games of childish make-believe, it's that she's shown herself how actively debilitating her fixation with childhood is.
Nostalgia is an amazing thing and there's nothing wrong with revisiting things from your childhood or embracing your inner child in moderation. But she's at the point where she's starved herself in a misguided attempt to look like a child (and just looks withered and elderly now). She said she has panic attacks when going out to socialise with adults. She says she went to therapy because she was terrified of being alone in the house, declared herself cured after a few sessions and then spent the years since shackled to her parents, with daddy tracking her on GPS and mummy never more than a room away.
She refused to learn to drive, to move into the house she owns or to make new friends who weren't either related to her or children of her parents' friends, so 95% of her social interactions are either with mummy and daddy there, or with children she's befriended online, which is beyond weird in itself.
She's cocooned herself in her bedroom trying to recapture her youth with her child's bed, her child's desk, her multiple murals of children on the walls while she dresses like a child and does childish things, telling childish lies about how precocious she was when she was TWALVE. Even her classroom "job" seems like a desperate attempt to relive her school days. And none of it is doing her any good. She doesn't seem to genuinely enjoy anything that she does and her physical and mental health have been progressively withering away for years.
This gap year should've been a time for her to cut the cord, learn to grow up and be more independent. Instead she's just regressed further into childhood and now she's completely unequipped for adulthood and her life is in a pathetic state - more childish bullshit isn't going to do her any good.
I used to live in Düsseldorf, now I live between Duisburg and Krefeld, so Niederrhein, i.e. almost like the Rhineland. Carnival is a big thing here. 
