Bank Question regarding paying off a loan account and closing it?

What is the deal with having to pay a fee to close a loan account. My Mother's Bank would not let her take out a loan at 68 but they kept her loans open even though they were paid up and even though they knew she was not able to take out any more loans. now they want to charge her quite a large sum of money to close those accounts... Is that legal and what are they charging her for? As it is there are all sorts of interest amounts and extra fees added on to the original loan and then she must still pay to close them off.