Hi Mike,
You might want to review this
threadon human "flaws".
Irregularity in features isn't really a flaw, it's a difference from the norm. As I mentioned in the referenced thread, I think you should, assuming this is a commission, just ask her. This is also the reason that I ask models, before I do the photography, to tell me the two things they like best about their faces, and the two things they like least.
When the difference is as pronounced as in Melanie's case, if you match either eye you'll lose her likeness. An alternative would be to re-photograph her with a 7/8 or profile viewpoint.
If you are doing this strictly for a portfolio, then you should probably match the eyes.