So let's put the shoe on the other foot. This model contacted you and wanted to pay you some money to do some portfolio shots. Time, date, location, cost all agreed on.
You, as the photographer running a business, do what you have been paid for and she comes back for a viewing to choose her images.
Now you as a smart business person ask her if she would like to upgrade her package, maybe include an album with extra images in. Yes it's going to cost her more money, but hey ho, you are running a business, you have to ask the questions.
Now how would YOU feel if she subsequently went onto a forum and totally slated you? You had agreed a price, you had agreed a service and now you were trying to sell her something else for more money.
You'd be pretty peeved wouldn't you? All you were doing was trying to run a business and earn a living.
So, what exactly, is the difference between what she has done, and what you would have done? You are both running a business, you are both trying to earn a living.
Just something to think about!