My sisters betta fish

Question
My little sister's betta fish has had a swollen stomach for a while. We believed
it was because she was holding unfertilized eggs. Now however, I think that
she has some sort of disease, because her stomach is torn along her side. She
has a big hole from which white stuff (or insides) is coming out. The betta
seems to not care at all, but I am still a bit scared that this might kill her. The
white insides coming out are still attacked to her body, but seem torn. I know
there may not be a way to cure this, but I would like to know what it is and if
there is a way to keep it from killing the betta if it is life-threatening.

Answer
Hello,
Your betta has fungus, and if her belly is swollen, she is constipated too.  Constipation leads to Swim Bladder Disease.  Fungus is caused by poor water conditions.  Water changes are so important to the Betta, this must not be neglected.  Swim Bladder is caused by poor diet, and overfeeding.  
You must treat her for fungus right away, or you will lose your little fish.  Fungus eliminator by Jungle is a good product to use.  There are also other products such as Maracyn.  You may obtain good results with a combination of Fungus eliminator, and Melafix.
Change all the water in her tank before using the medication. Use a good water conditioner, such as Stress Coat, or Aqua Safe, and make sure that her new water is the same temperature as the water she was in.  The fungus is eating her alive, and will eventually kill her if left untreated.
Feed her a cooked frozen pea.  Remove the first layer, and cut it into tiny pieces.  Feed her the pieces one at a time, making sure that the pieces don't fall at the bottom of the tank.  This is to help her clean out her system.

Here is some information on the Betta fish, and how it should be kept:

A betta needs 5 gallons of water to be healthy, and happy.  
In their habitat the betta may live in shallow waters, but they have lots of room to swim.  
Keeping Bettas in small bowls, containers, vases etc, is cruel.  The Betta is one of the most mistreated fish on the market.
They need a heated tank.  Temperature should be 78-80 degrees.  They are tropical fish, and are cold under this temperature.  Cold bettas get sick, are miserable, and live unhappy lives. ( Always remember  when heating a tank, do this very very slowly..1 (one) degree every two days, as bringing up the temperature too fast would kill your Betta.)  The temperature should always be stable.  Fluctuating temperature is very bad for bettas, and any other fish.  
They should have a silk plant in their tanks, so that they can rest on the leaves  They also need a little tunnel or some knick knack that they can go through.   One teaspoon to five gallons of diluted aquarium salt may be added to his water, when a Betta is well.  
Aquarium salt helps them with stress, and helps with parasites.  However if a Betta is showing signs of a swollen tummy, salt should not be used.
They need a varied diet. This is very important.  Betta pellets one day, Betta Flakes the next, Daphnia the next, and bloodworms should be given once a week as a treat.
He should be given one well cooked frozen cooked pea a week, and on the day you give him the pea, he should fast.    
A betta is prone to constipation, and constipation leads to Swim Bladder Disease.  A pea a week keeps them from getting constipated.
They should have 2-3 small meals a day, and not one big meal.  We must remember that their tummy is the size of their eye.
Example:  2 pellets for one meal.
Water changes are very important.  Water changes must be made every week without fail with a good water conditioner such as Aqua Safe or Stress Coat.  There is also a conditioner made especially for bettas.   Never put two bettas in the same tank, they will kill each other...male or female.  The Betta male is a loner.  Females can be kept together in a big enough tank.
When treated well, a betta can live up to 8 years, if you buy him when he is very young.  (Unfortunately we do not know their age when we buy them at the Pet Store which is why some bettas die two or three years after we have bought them.
He's an intelligent little fish, and should be treated with kindness.
Too many vendors know nothing about the betta, and don't care...so don't give good information on how to keep them.
They are there to sell, and will say anything just to make a buck.  They send you home with your bought betta, telling you a small bowl is perfect, and bloodworms!  The poor customer thinks he has everything he/she needs, and then the fish gets sick, money is spent to cure him, and eventually the fish dies.   
This turns my stomach over.  Unfortunately there are no laws to protect fish.  
Bettas kept in small bowls, one gallon tanks, and vases, will get sick, and are very hard to cure in such little water.  They end up dying, and
that hurts the person who has grown so attached to them.  They don't deserve to be treated this way.
This is how a Betta should be treated.  If treated this way, you will have your friend for a long long time.  I have bred them, love them, and know what is good for them.
I hope this helps, and she will pull through.  If you have anymore questions do not hesitate to ask me.
Lynda