I'm writing a novel in which the protagonist starts to become suspicious of her mother's involvement in a hospital scandal that has to do with the protagonist's love interest. The novel continues in a pattern of acquiring clues to eventually come to the reason for her mother's suspicious activities.
I don't have any other suspects which makes me worry that this book isn't very surprising. I'm worried that the events that happen won't totally surprise the reader since it's expected that her mother has something to do with the incident. Does this count as being a mystery?
It sounds to me like you might actually be writing Romantic Suspense.
Romantic suspense involves two elements.
1. Suspense. There is a trap being set for the main character, or possibly she is being stalked by a villain. The reader senses the danger approaching and worries if she will escape in time (which she does).
2. Romance. Key to her escape is a romantic plot in which she must learn to trust her potential lover. There should be a sort of dance in which sometimes he seems trustworthy and at other times there is reason to suspect him of being a villain. Of course, he will turn out to be a good guy, but the mystery is generally kept up until near the end. (In some romantic suspenses, the heroine has the choice of two potential lovers, one of whom is the villain and the other is trustworthy, and she has to make the right choice.)
As you can see, these are different from mysteries, which are generally about solving a murder. In romantic suspense, the crime has not happened yet, but will if the heroine doesn't put the pieces together at the crisis.
The truth only comes out at the crisis, when the trap springs. This is usually followed by a chase that ends with the heroine escaping and the villain caught or killed. These days, it's common for the heroine to defeat the villain herself, but sometimes police or other allies can help.
Hope that helps.