Seems the "ice" wasn't really stable ice but only enchanted water and "melted" when the spell failed due to sorcerer no longer being present. Sloppy work. If she actually lowered temperature, it would stay longer, even if it's summer.
@hkmaly: Yup. In this case this was water from the garden itself. In chapter one, it was magically created water, which is why it stuck around ^_^
She didn't bother with Linne, since she doesn't consider Linne a threat so she didn't here.
She mostly did it to the guards to keep the town busy, in addition to setting all the fires because as incompetent as a castle guard might be, giving them time to unite and give chase is never a good idea, lol