If it's a real book, she knows that it probably wouldn't get published if it were no good. She knows it has been spell-checked. With an e-book, these assurances are not there. Anyone can slap an e-book together and offer it for sale. She also ends up with some data on her hard drive - not a book in her hands.
People simply like to hold things they buy.
Many people shop to feel better. There are a couple of effective ways to add to the perceived value of information products. You can also add to the perceived value of information products by increasing the price . Every product has a level of price resistance. The ideal is to find yours by experimenting and then set is just below that mark.