Your translation is clear and precise, but here is a slightly "tweaked" version :cherine said:Her mother was mad at her because she refused to help her sister in preparing dinner. (of course you can put it in better English)
Josh,Josh Adkins said:I forgot to give the context. This is just a sentence out of an Arabic textbook.
This is just a simple sentence, but the reason I asked for translation is because I was wondering how others would translate it.
غضبت والدتها منها لأنها رفضت مساعدة أختها في إعداد العشاء
The underlined part is what interests. We all know that مساعدة is a مصدر (maSdar). Now, the maSdar can be used in an infinitive fashion after a verb, such as:
رفضت مساعدة she refused to help
But مساعدة can also be used in an إصافة (iDaafa), or genitive construction, such as:
مساعدة أختها her sister’s help
So the sentence could be translated as:
Her mother got mad at her because she refused to help her sister prepare dinner.
Her mother got mad at her because she refused her sister’s help in preparing dinner.
Of course these two sentences have different meanings. So, in this kind of wording, where a verb phrase or a possible iDaafa construction are both possible would the maSdar be preempted by the verb? Most people would probably translate the sentence the way you guys did, so I assume it would, or at least, that's how people would interpret the context.