OP you sound like the nicest person. Every post on here is thinking about everyone else. It's quite interesting you have had a unanimous response that your DD is being quite normal and understandable in her response here. It's an interesting thread as it's an issue you don't see raised a lot.
I'm not sure whether chasing the same things for your DD is the best approach as she will always be second in those, whether it takes a year down the line or whatever. The device sounds good and worth pursuing. Will she care so much about the shoes in some months or is it more a symbol in which case it might stay that symbol if she gets these things second after a long time and lots of effort? I wonder if she needs more acknowledgement from those around somehow and whether you could ask the school to do something for her. Even if it's just make a nice speech or something. Are there specific things that you could maybe organise for her? It might be they don't have to be so expensive. It sounds more like it's the sense of the outside world caring as much as the thing itself that upsets her.
Like others have said, I'd join in with her feelings maybe. Yes it isn't fair. She should be allowed to say it and feel it. As someone said, she probably has a lot of feelings pinned onto these symbolic things and it probably isn't just jealousy as such but all sorts of complicated feelings about being cared about, recognised, what she's going through, feeling part of things when she's out the loop a lot, being with her peers, whether she fits in and maybe some fear of the future. All these things. Maybe although it's very painful it might allow you to start letting her express some of that in a safe way?
In terms of explaining the situation, the simple explanation I suppose is that her condition is not known about and people don't know about it or understand it or how hard it is. Whereas cancer is a more common condition, sadly, and so people have more of an immediate understanding of what that means. So it is not at all about individuals, but about what people understand.
In terms of doing things that could make her feel special, is there anything you can organise that might help make her feel this? The shoes thing might be more fun if you could take her to paint them herself maybe or is there a way that maybe you and her closest friends could organise a party or event for her. Just because. Take her somewhere fun, or do some making of things together or whatever she enjoys? I know that's all cost, but it might be more the recognition and a bit of spoiling that is more important anyway, but sounds like involvement maybe from some of her friends or peers could be most helpful?