Fucking hell!
Why she smells has absolutely fuck all to do with you, thats her business and not for you to pontificate on, decide it is because she's morbidly obese or doesn't wash or anything else.
THAT she smells is something you should take to the appropriate person - probably her manager.
Thats it, end of, the rest is none of your fucking business.
Anyone can smell.
Some people smell because they do not wash properly, for a wide variety of reasons that may include being unable to, lacking the facilities to do so, lacking the physical ability to do so, or even because they just can't be bothered.
Some people smell because despite washing properly they have skin conditions that you can't see, that can produce a fucking foul odour in a matter of hours, and cannot be masked.
I had the misfortune to suffer a skin infection in my armpits - NOTHING touched it, could wash and it'd still smell, five minutes later, suppurating mess, smelt like dead things. Couldn't put anything on it, that made it worse. Dried it out using a hairdryer on the cool setting - still wet and gipping in minutes. Absolutely fucking awful and it took nearly 4 months to clear up. Piss all to do with washing, I washed it at one point every bloody hour, I went through clean bras and t-shirts like you wouldn't believe.
It took a combination of antibiotic creams and tablets (specific, had a horrible skin scrape) and anti-fungals to clear up in the end.
So, report to your manager then mind your own business!