To be realistic, the odds are stacked against her, because of her 'N' level academic background, and (this applies to all Singaporean students) because of the overly small number of places available in local medical schools. And if her medical condition does not resolve itself immediately or fully (only her oncologist will know her medical prognosis), it may continue to post further financial and time burdens that may distract her from performing her best along the way.
However, should she indeed perform spectacularly well (ie. perfect scores for all subjects and all modules all the way here on out), her 'N' level academic background and her bone cancer medical condition, could actually help her stand out amongst the pool of candidates vying for a coveted place in medical school, as positive indications of her tenacity, perseverance and determination.
Of course, the rich (especially ultra-rich) will always have multiple advantages over everyone else. If her family can afford it, then applying for overseas medical schools (of which there are thousands, though only a few dozen or so are recognized for practicing medicine in Singapore), in addition to local medical schools, will naturally increase her chances of fulfilling her career ambitions. And if you're rich enough to locate yourself overseas permanently, you could even go for medical schools not recognized for practicing medicine in Singapore, as a last resort.
I wish her all the best in her health and in her medical doctor career ambitions.