I'm in agreement with the other responders who say, if you can, have her evaluated by a psychologist outside of the school.
Her tendency to smell things may or may not have anything to do with her stuggling in school. A competent psychologist should be able to help to sort this out. This behavior can be a part of a sensory processing disorder, or not. To be diagnosed with this, a person needs to display a certain number of a list of behaviors, or the behaviors need to interfere with their lives.
I've looked into the symptoms of this disorder and my daughter and I both display some of these behaviors (sensitivity to smells and/or tastes, teeth brushing aversion (more than usual for a kid), sensitivity to clothing, etc.), but not to a level that interferes with life. I've had to learn not to smell things so much in public...