Questions & Answers about Die wysie is mooi.
Yes, it has a diminutive form.
Afrikaans very often uses endings like -ie, -tjie, and similar forms to make nouns smaller, cuter, or more informal. In the case of wysie, the word is commonly used as the normal word for a tune or little melody.
So even though it has a diminutive shape, in everyday use it does not always need to sound especially small in English. Often you can simply translate it as tune or melody.