She said she couldn't top it - not that she wasn't good at it. She also said that she was topping 2u maths, which obviously indicates that she's at least somewhat mathematically competent.
She wouldn't have to top it in order for it to count/outscale something like Biology, or Economics, since...
Nope.
You can tell because the top 100 schools have the 'legit' rankings posted up, and those are significantly different in some cases e.g. Sydney Technical is 15 instead of 23, Hurlstone Agricultural is 34 instead of 26 etc.
Yet again a misconception about scaling.
You seem to enjoy humanities more?
Economics outscales Physics and Chemistry.
So I reckon considering scaling (which is an important thing to consider in my opinion), go for:
3U Maths
2U Advanced English
2U Physics
2U Economics
2U Legal Studies.
2U...
No it doesn't. It scales worse than most other Science, Maths and HSIE 2 unit subjects.
Source: http://www.uac.edu.au/documents/atar/2011_HSC_Table%20A3.pdf
Since we all know that you're pretty pro at maths/science, your ATAR will be determined by your English mark. I reckon you'll cope with 10 units. If you reckon that keeping Legal will harm your English, then drop it. I'm pretty sure that given your skills and your interests, MX1 + MX2 + Phys +...
Don't know about ESL, but Standard is around 87 I think. Although since ESL aligns better than Standard, it would be lower, maybe around 83.
Oh, and these are out of 100.