Photography

The short and blunt answer: you are wrong.

You say your wife is an artist so you understand the value of her experience and equipment all had to be considered in pricing her work. Well let's assume shes a painter and she is commissioned to do a painting for someone. She is paid a fixed fee for 1 finished painting. She goes through 3 canvases trying different approaches to the commission before she presented the finished piece to the client. They then insist that they are entitled to all of the other canvases too and act outraged when your wife insists that they would have to pay for her to finish them if they wanted them. Sound reasonable?

This photographer was paid $1800 for make-up and wardrobe, 2 hours of studio time with a skilled professional, post processing time to "finish" the images and 15 finished images. The images taken in the studio don't belong to you. The 15 you paid for belong to you (with certain rights retained by the photographer). It's standard practice to be given a proof sheet of low res watermarked images for you to choose your preferred images (personally I wouldn't provide 300, thats choice paralysis territory for a lot of people, but I digress). If you want more, that's got to be paid for. That's stock off the photographers shelf and further time and effort to finish the additional images.

No self-employed photographer who wants to stay in business will ever give or sell unfinished images to anyone. Asking for unfinished images is like getting your bathroom remodelled but asking the contractor not to fit any faucets or fixings. You'll have to do that yourself or get somebody else to finish it and the work likely won't be up to that contractors standard. If anybody else saw the finished bathroom, they will likely conclude that the whole of the remodel was done by the contractor, including the shoddy finishing, and their reputation and business will be negatively impacted as a result.

In short, you get what you pay for. If you want more, you pay for it.