Tutoring isn't necessary for English imo, I came to Australia 8 years ago with 0 English, never went tutoring and ended up with a 92 in Advanced :S Never listened to teachers telling me to read books lol, in the end just learn how to write essays and memorise them for year 12, that's basically all I did.
Maybe she studied without telling you. I know some people that work hard and tell nobody, not because they are modest or anything. I guess some people would even tell others they don't try so they wont feel as shit if they dont get what they expected. Cynical yes, but these people are quite common.