Why would anyone's mortgage go up $300.00? Mine has been the same for 21 years. It hasn't varied a dime.
Now, if the teacher was stupid enough to sign for a variable rate mortgage, well, she should be paying less. Rates have gone down in most areas.
So why, oh why, did this teacher's mortgage go up $300.00? Property taxes? Not likely. Home values have been steady or turning downward just about everywhere. Regardless, a $3600.00 per year jump in taxes is very unlikely.
Maybe her insurance went up $3600.00? Equally unlikely. Unless she burned the house down last year.