An interesting variable there though is the plastic cup- it is well known that the vessel a drink is in affects our perception of the taste, so it is no surprise that she couldn't recognise her favourite cola or indeed the taste of the other colas, because they are all either drunk from clear plastic bottles, glass bottles or from glasses. As a child and up to early adulthood I was in the habit of drinking milk with my dinner, always from a mug. I have never liked milk from a glass bottle, for instance.No methodology. You also need a much bigger sample size, and perhaps a longer testing period. E.g. it has been proven that sweeter drinks tend to be more appealing here and now, but not necessarily in the long run.
It was for fun because someone said she only drank Pepsi Max, and distasted Coca cola, incl. zero.
It was the four colas, diet and regular, in newly opened bottles poured into 6 plastic cups marked with numbers only. (So two of the cups had the same in them).
Funny thing is she thought the same content tasted differently. It was almost random guesses.
I must admit I also tried and got 4 out of 6 right, even though I didn't think I could taste the difference. But it could have been luck. 25% chance of guessing right with each cup. Hence the 6 cups and not just 4.