I think two parts of the brain are talking just fine... but it's not the logical part that wins the debate.
Like you said, she's a foodie. This is probably less about whether she believes Soylent would be healthful, and more about the fact that she's unwilling to give up the variety of foods and flavors she currently experiences. Calling "Soylent" yucky may, in fact, just be code for, "I really love the things I'm eating now."
A lot of people love their food experience more than they want to be healthy. Our bodies are, in many ways, hard-wired to love our food experiences. This is a profound thing to overcome.