Why is the sentence "She is struggling from an illness" incorrect? I know the correct sentence is "She is struggling with an illness", but "struggling from" just sounds more natural to me.
This expression has more inspiring context behind. "Struggling with illness" sounds like you're strong enough to fight and win while "struggling from smth" associates with the action when you're trying to fend off. But this is just my opinion.
E.g.: Footballers struggle with injuries.
Footballers struggle from poor form.
In my opinion based upon my research,"struggle" can be used as verb or noun. Now, I am explaining usage of "struggle" as 'verb' in detail:
Usage of "struggle" as verb:
1.a) struggle + (for something): It means to try very hard to do something when it is difficult or when there are a lot of problems. e.g, a country struggling for independence. Here, struggle is coming with 'for' + 'something' is independence.
1.b) struggle + (adverb/preposition): to move somewhere or do something with difficulty. e.g, He struggled out of his wheelchair.
1.c) struggle + (against/with somebody/something): to fight against somebody or something in order to prevent a bad situation or result. e.g, He struggled against cancer for two years. OR She is struggling with an illness.[Your Query's Answer is 'struggle' + 'with' + 'something']
1.d) struggle + (with somebody): to fight somebody or try to get away from them. e.g, Tim was hit in the mouth as he struggle with the enemies.
1.e) struggle + (with somebody) + (for something): to compete or argue with somebody, especially in order to get something. e.g, I am struggling with my neighbours for my property.
If you need the usage for "struggle" as a noun, I can do it.