No that accident was not explained until the last part of this manga. Actually it will happen in about 2-3 chapters. So yes she does not know it.
Ye she’s an adult. A very irresponsible one. She was just always reading books. She took classes to become a librarian. Even on this life she shows how irresponsible and selfish she is.
The trombe one being able to replace tools will be discussed by the manga itself though not for a very long time. Also its not known by anyone that trombe was actually sucking magic, except to us the readers. Which was also a secret until it was spoiled by people like me