That is not only French, I think, because otherwise chances are that your sister will die soon of dehydration...
When you place "ever" at the end, you put an emphasis that is not meant in the French sentence.
so, you have to stick to the style of the French with "my sister never drinks/does not ever drink".
"my sister does not drink ever" would rather be "ma soeur ne boit absolument jamais" or something of the like.
"bois" is the conjugation for "je" and "tu".
3rd person is il/elle boit.
Negations come in two words: ne... par; ne... plus; ne... jamais; ne... rien; ne... aucun; ne... personne
You cannot have 3 negative words around the same verb.
- my sister never drinks (= my sister does not ever drink) = ma soeur ne boit jamais
- my sister does not drink = ma soeur ne boit pas
From what I understand, the "jamais" replaces the "pas". The "pas" being the English equivalent of "does not" whereas the "jamais" being "never" (it doesn't quite directly translate, but you get the idea). I am still very much a learner so someone please feel free to correct me :P But this is how I have understood it.
Can any French speaker confirm how the sentence would sound to them? Would it be kind of like: "My sister does not drink never" - or is it kind of untranslatable?
The fact that most of the time 'sentences like she drinks' is accepted as is 'she is drinking', I would expect that "my sister is never drinking" to be a solution as well? Anyone?
No, that doesn't work in English. I can give a more detailed treatment if you like but the short version is that you can't have "progressive present" here when going to English.
Why can't it be, "My sister doesn't drink." I don't understand how we know "ne" means "never" in this case.
What have you done with "jamais"?
ne... jamais = not... ever OR never.
No, it is just than French negatives are formed with two words: "ne" + pas/plus/rien/aucun/jamais/personne.
"Ma soeur ne boit jamais" is not more a double negative than "my sister does not drink ever".