Sympathies mate, for sure, but she's still gets a "you're doing it wrong". Get in shape first, start slow, drop the pounds, THEN exert yourself.
And it's not like I'm saying she's to fat to be a model. She's too out-of-shape to engage in a grueling physical activity, it's dangerous and irresponcible, and I hope there has been a waiver involved somewhere. This isn't Gattica, it's sense.
Hypothetical: Rowing, tired, exhausted... asthma attack, collapes into water, lungs full of water, too heavy to be easily hoisted out by rescuers, dead. This is a very real possibility, you have to balance those boats because they're so narrow.