It's not a deep cut, but kids aren't known for their great tolerance to pain.
Hopefully she will remember to be more careful around broken glass.
The bit about fairy memory showed Aster not remembering at all what had happened with a troll, but remembering that trolls were dangerous, so the notion that glass can hurt would still stick. Though the current situation is unlikely to trigger fairy forgetfulness, Myces seems a lot more offended than scared there!
I feel sorry for her :s
Don't worry, she'll be better soon...
If she doesn't keep doing dangerous things!