"...but she soon realised that school-teaching was not her métier..."
Métier means a trade, profession or occupation. It also means one's forte. Interestingly, both métier and forte are French words. Before being French, métier came from the Latin ministerium 'service'.
The WREAK in WREAK HAVOC comes from an Old English word meaning to 'avenge'. Increasingly, it's being wrongly used as 'wreck havoc'