Obese isn't really up for debate. Its a percentage of body weight and it is what it is. 50lbs is obese if your 5'5, not if you're 6'5. well, 6'7. But its close...for the math, see here:
http://lowcarbdiets.about.com/librar...yfatcharts.htm
aside from the hard stats, which (lets be realistic - aside from professional athletes) there are few exceptions, its about preference and desire. Of course most women aren't dying to have sex with someone 50 and 100 lbs over healty weight. While facts are facts, there are of course components of a person - personality, kindness and intrigue that have an impact on superficial factors.
But I agree, someone who is significantly overweight (and you know if that's you, if you don't, your problems are about denial and weight is just a side effect), its probably for the best if you share it. If for no other reason other than it provides an opportunity for vulnerability. If you can't be accepted when you're vulnerable with her over email
before you meet her, frankly, who wants the intimacy afforded in a 1 on 1 exchange?