as a native speaker i can't see much difference in everyday conversational speech, I guess the three versions feel a little different. but you don't need to worry about it unless you want to study literature. The one that stands out the most to me is the third one, it sort of implies she asked ONLY you for help and nobody else. I think there are three because Help can be treated as a verb (something you do like in the first one "to help") and it can be treated as an object (something you give like in the second two "for help, my help"). So don't worry about which you use, all 3 are good in any situation.

The other answers were good too, but also look at it like this: She asked me to help. - She is asking you a direct question for you to help. (She asked me to help her with English.) She asked me for help. - Think like this: She is learning English, but wants your help. Not someone else. She asked for my help. - Think like this: You are talking to a friend and telling them that, She asked you to help her.

They are all correct and all of the sentences have the same meaning. 1) 'She asked me to help.' - would most likely be used in a scenario where you are helping a group with something. 2) 'She asked me for help' - would most likely be used if she was asking your advice or something. 3) 'She asked for my help' - would usually be used if she was asking you to do her a personal favor.

1 后面往往接人物 to help her 或者 to help him.表示她让我帮某人 2 很简单 表示她找我帮忙，寻求帮助 3 同样表示找我帮忙，但特指“我的"帮助，不指别人的帮助