"Weak" is, as we usually understand it, "schwach" in German, and "bad" is "schlecht". However, depending on the context and the sentence construction the same word can have different meanings. I don't know exactly why Duolingo has chosen "weak" as an alternative, but I imagine it could substitute for bad, as in "that was a weak argument".
"She ist schlecht" means "she is bad". If you would like to say "she is sick / unwell" you would say in German "ihr geht es schlecht" (literally: "To her it goes badly"). You might also say "ihr ist schlecht" , which means something like "she doesn't feel well" or "she is nauseous / queasy".
ihr can mean all sorts of things, unfortunately! It all depends on which case it is in and whether there is a noun after it or not...
Have a look at this comment I wrote elsewhere: https://www.duolingo.com/comment/21721534$comment_id=23831061
It instead of She would be, 'Es ist schlecht'. Translating as 'it' would be incorrect as 'it' assumes genderless or an unknown language essentially losing the subject's biological gender in translation which would be awful for her if she was then mistaken as a male. ;)
Es = it Sie = She/They/You (formal) Er = He
Remember, the genders of nouns are unrelated to that of any biological sex (Ein Mädchen, for example).
The first letter of every sentence is capitalised in German as in English.
So when it's the very first word of a sentence, you can't tell the difference between sie and Sie.
Sie ist schlecht. can only mean "She is bad." because of the verb, but Sie sind schlecht. could mean either "They are bad." or "You are bad." -- you can't tell the difference between those two since sie/Sie is the first word.
If there is something before it, then you can tell again, e.g. Deshalb sind sie schlecht. "That's why they are bad." versus Deshalb sind Sie schlecht. "That's why you are bad.".
Yes, I am aware of this, I know the difference in meaning and spelling. But as this is a listening question you have to translate what you hear, how do you know that it is 'ist' as opposed to 'isst', as they sound the same? Of course I knew that it meant 'ist' because of the rest of the exercise, but want to know if the other alternative would have been possible
as this is a listening question you have to translate what you hear
I've seen "type what you hear" questions (audio German -> written German) and "translate" questions (written German -> written English), but haven't seen any "translate what you hear" exercises. Are you sure that's what you had? Could you provide a screenshot? (Upload it to a website somewhere -- e.g. imgur -- and tell us the URL.)
want to know if the other alternative would have been possible
In natural German, ist would probably be unstressed (sie ist schlécht) and isst stressed (sie ísst schlècht), but I wouldn't rely on the text-to-speech "robot voice" to make this distinction in a natural way -- the two sentences might well sound completely identical.
Okay, sorry, I wrote that wrong, it was a write what you hear, and I was wondering if it would be correct to write Sie ist schlecht AND Sie isst schlecht. I didn't try the Sie isst schlecht, as I knew what the exercise was about, but wanted to know if Sie isst schlecht would also be correct just from listening to it. As far as I could hear there was no more stress on either word, so indeed I guess this would be easier to judge in a conversation.
it was a write what you hear, and I was wondering if it would be correct to write Sie ist schlecht AND Sie isst schlecht.
That's a good question.
I don't know of any way to submit more than one correct answer for a listening exercise, and I don't know how listening exercises are graded -- if only against the German sentence or whether there's a bit more "intelligence" that knows about words that are pronounced the same but spelled differently.