Sinalta was born with a large mana pool, enough to activate the measuring device in the castle or the adventurer guild, any other lesser version would have shattered from the sheer amount of mana she possessed.
She was blessed with the use of multiple elements air, fire, earth, metal and light.
Being able to control three of the five base elements and five elements in total she was considered a prodigy, nothing unexpected of a noble.
As a princess, she had a room that had more or less the same effect that was given to the whole old building of the school.
The magic circle underlying wasn’t something particularly complex, if anything it was the basis of the development of the measuring device in any size, a magic circle that allowed the collection of mana.
If there was a difference, it was that this circle concentrated it inside the owner of said magic and not in a device for display.