I can imagine how hard it must be to see her go through those tests and checkups for her health, but the important thing is that you as parents are there for her supporting her as much as you can and making her feel loved, that is the best thing she can receive. She seems to be a smart, brave, and determined girl, a little trooper as you said. I'm sure when she showed the bandage to her friends at school she felt very important. And it's cool that she likes chess and math.
As for the 1400 euros that's a lot and well here it may cost less but salaries are miserable, public health sucks and private medicine is expensive for most, plus insurance even if you have it only recognizes a part of the expenses. I still have some bills to pay that the insurance did not cover when I was in the hospital two months ago.
I don't remember doing this kind of thing as a kid. I didn't really do the show and tell thing, though I didn't have friends!
It is the same here. We are unsure what they will cover out of this, but hopefully "most of it" because 1400 is a lot :)
It is these kinds of "debts" that can slowly bury us, if they come one after the other. At times though, they are unavoidable and then, we just have to deal with them. Good luck.