She sounds like a lucky girl, and I'm sure that youre doing a better job than you give yourself credit for on the post! ;) Even just with all the speaking practice and personal attention I'm sure she's getting with your lovely family, that she probably wouldn't normally get back home.
I see you've already identified certain problems she has with the language.
With regards to pronounciation I'm guessing she's probably familiar with the phonetic table and symbols.
You could try to help her with problem sounds she has and see if you can improve them somewhat.
Here's the first from a series of clips from Adrian Underhill (it's on youtube) about pronounciation. It may be interesting....
YouTube - Adrian Underhill on Successful Pronunication 1 (Macmillan)
- For Teachers