Please can anyone tell me what "a witch to boot" means?
'to boot' is an archaic and/or poetic way of saying 'also'.
Of course, saying that is an invitation for other teachers to say 'but I use it all the time'. Maybe archaic is the wrong word: 'to boot' is a rather mannered way of saying also and giving it emphasis: 'He is a teacher, and a good one to boot'.
A witch is just a witch.