"In Ikimashou, Casa Loma and the surrounding George Brown College are the sites of an imaginary school. Dupont station is nearby, no?"
The only thing I'd then argue is that it shouldn't be referred to as a university, as George Brown is a college and colleges aren't seen as on the same level as universities. Now I get that this is suppose to not be 1-1 copy of real life, but I'm generally of the opinion of "if you can make it closer to real life, why not?" It creates a bit of familiarity for people who either already know the locations (like me) or who play the game and then end up visiting one day. The only thing you'd need to do is avoid using any sort of names that could be copyright (for example, the George Brown name) but could still refer to the area.
Also with regards to Toronto Island, I'd still argue she should travel east to the ferry that takes you into the actual island since that's what her plan is. Getting stuck in an airport seems silly, y'know?
I'd fight you if I could for BeaverTails.
Ok, so I'm now going to take the time to do the thing that I've been wanting to cover for a while with regards to her just taking off (and why I think it's important that certain things be changed or done to make immersion better).
First, there's the issues her age would cause (which would result in a lot of legal issues). If she's a minor, then her doing certain things just... wouldn't/shouldn't be possible such as buying train tickets or getting a room at a hostel. I can't remember for train tickets offhand, but I do know that for hotels and hostels that you'd need ID, and the moment she flashes an ID that says she's underage there's going to be problems. On top of this, there's the fact that her adoptive mother would likely call the police and report her as missing, at which point her identity would likely be spread across Canada to various police to try and find her. Now whether they do is another question, but it's bound to be that someone, somewhere, will recognize her. For these reasons, I think it's important that you define her as being of an age where she wouldn't be questioned. This would have an impact on her "school" stuff, namely because you'd have to likely make it that she was done school, but personally I think this would be better.
Second, there's the financial issue. From the story presented, Zinnia's adoptive mother doesn't have a lot of money. Similarly, it doesn't sound like Zinnia worked some sort of part-time job to save money up as she instead spent all her time going on adventures. So how is she affording all of this? There should be something to explain how she can afford this. Personally, I think the plot point around Zinnia's adoptive mother not having a lot of money should be dropped (I also think the tuition thing should be dropped) as it adds to this problem.
Third, safety issues. First, Zinnia is a girl all by herself, going to a place where she knows nobody. I feel confident you can agree how dangerous that can be. While it's obvious that Zinnia can be an airhead, I feel like she should be smart enough to know to keep herself safe. It doesn't need to be something you actively show in the story but instead be based on her choices.
Personally, when I look at these issues and how to fix them, what I see is this...
Zinnia should be between high school and college/university and be at least 18. She should have been saving money for some time now (Maybe she took on a part-time job in her last year of school, then took on more hours once school ended). The issues between her and her adoptive mother could be because the latter wants her to get into college/uni right away but Zinnia wants her adventure first. After she saves enough, she puts in a two-week notice and, at the end of it, takes off. At least in this scenario, you deal with her age, the financial side of things and also that her adopted mother knows what she's doing and can't fully call the cops to report her as missing (maybe Zinnia should also text her mom every few days so her mom knows she's okay. This would be one of those things to show she's trying to keep safe). While this may not fit what you wanted it to be for her, it would at least make more sense and there's nothing wrong with having a bit of realism considering you're going through actual places in Canada.
And just for context to all of this... I do story writing myself, with one of my stories being based in Toronto. Even though the story is a magical girl one, I still try to keep realism there and keep whatever aspects of Toronto that I can intact.