Obesity and Marriage

Hi. I am from India. I have a problem concerning my sister. Obesity runs in our family. My sister (25) and me(27) are both obese but not morbidly obese. In India the culture is that the family get the girl married in her teens or maybe in the early twenties. We followed the same pattern but because of her weight problem she was rejected with prospective matches. This has made her more depressed and once tried to commit suicide. Now that we have found a match for her, she is not happy with the match as the guy is not educated according to her standards and also is fat.

But the brutal system in India is so bad that an unmarried girl is looked down upon so we are going ahead with the marriage. Even my sister has agreed to go ahead with the marriage. But its like she is on a retaliation. She is a BS in applied nutrition and used to watch her weight carefully (even though she could never lose much weight). But now its like she is on a eating spree and has gained around 10kgs in the past 6 months. The marriage is scheduled to be in June/July and we are afraid that she will gain more in that time.

No matter how we try to talk to her, she does not listen.Its like she wants to take revenge for setting her up for such a match. Whenever we try to talk to her, she acts as if she is not hearing us and starts looking at the walls or the roof and sometimes comes up with rude replies.Last night we tried to ask her why she is not controlling her diet to which she replied that she wants to eat her way to being a diabetic so that she can die soon. We are helpless. A little more about her past: Since we were overweight since childhood, we has been at the receiving end of peoples jokes all the time.

Also my father's attitude towards her is not as pleasing as the attitude towards me and my brother. We tried talking to my father but he doesnt seem to like her that much. So now she almost hates my father and holds him responsible for everything. I am concerned that her behaving like this is not going to be good for her in the future. We thought about breaking up the engagement but that would leave a bad mark on the girl and would mean finding a suitable match for her would be 10 times more difficult (Indian marriage system is very very brutal). Please advice.
Thanx