We adopted our cat at 5 months old from a shelter. She has had blood in her stool since…

Many cats and kittens may have occasional blood in their stool especially if the stool is too soft or too hard. If the cat is healthy otherwise, and testing turns out o.k., I tend to not overreact. I think a diet change is a very reasonable thing to do at this point. Be sure to give the diet a chance to work; at least a couple weeks is ideal. This is something she could outgrow as well. I'd recommend keeping up a conversation with your veterinarian, express your concerns about more aggressive testing and see if you can reach a compromise that you're all comfortable with.