These can indeed by confusing terms, because they involve logically separating out things that in ordinary life we don't structure or analyze in the same way.
A good place to start is the Science Buddies discussion of variables --
https://www.sciencebuddies.org/science- ... bles.shtml
An example given on that page fits your case somewhat is: "The Independent Variable for Surveys and Tests of Different Groups." -- "When a scientist performs a test or survey on different groups of people or things, those groups define the independent variable."
In your experiment, you're doing the test over a group of people, so "the person" is a variable. Individuals might differ, and that's why you're testing more than one person, to get a sense of the range and commonality of responses.
You are also varying the foods they are tasting and whether or not they wear nose plugs. So those are also independent variables.
You might think of each trial as a combination of PERSON, FOOD, and PLUGS. (So you are right about PERSON and your friend is right about FOOD. But we also need to add the nose plugs.) In mathematical terms, we could describe the set of trials as { PERSON x FOOD x PLUGS } -- you have 6 people, 9 foods, and 2 plug configurations (on and off). That's { 6 x 9 x 2} -- you have a set with 108 combinations.
The dependent variable is what you are observing or measuring, the responses. I'm not familiar yet with your project, so I don't know how you're defining a response. Perhaps it is how they describe the taste. You hypothesize that the taste is affected by the food, the person, and the plugs -- so the taste depends on these other factors, it is a dependent variable. (So you were right here.)
Usually there is one dependent variable. Aside from what you deliberately change (the independent variables), everything else must be controlled. You demonstrate that you have everything under control so to speak to listing the "controlled variables" -- what you are being careful to keep the same in each of the 108 trials.
If you think about it, there are an infinite number of variables you want to keep constant! Some of the most relevant might be the temperature of the food, the order in which the food is tasted, and the time between each tasting. This is specified and summarized in your experimental procedure, which describes what you will be careful to do each time. (So your friend was right here.)
Understanding the types of variables, which this project will teach you, will be an important lesson for life. You will find it to be useful even outside of science. For example, how do we help homeless people? Should we give them housing, help them find jobs, provide free education? To solve everyday problems like this, we need to figure out what's the dependent variable and what can we vary that might change the outcome (the independent variables). So understanding how variables relate is really a basic part of learning how to solve problems in life in general.
Good luck with your project!
Bill