She makes the dinner is also fine in English, although as Albertyac says we do generally omit it in most contexts.
It may be specific to Brazilian Portuguese, but when I learned fazer in my class, we learned that faz was pronounced as [fais], not [faz].
In English you normally omit the article with "breakfast, lunch, and dinner". Examples: What did you have for breakfast? Where did you have lunch? She made spaghetti for dinner, not THE breakfast or THE lunch, or THE dinner. However, in Spanish, you CANNOT omit the article. I'm sure it's the same in Portuguese. So that's why we must use "o jantar".