A book where a girl disguises herself as a boy?

Kat Incorrigible it's about a girl who at the beginning of the story disguises herself as a boy to save her family from ruin only to be caught and she discovers shes a witch like her mother (who is dead sadly) and tries to save her sister from marrying a guy who murdered(it wasn't proved so he wasn't arrested) his last wife. She disguises herself as a boy several times in the book it's really odd.