I, my mother, and sister co-signed on a home for my mother so that she could afford a home she has been dreaming of for years. My mother paid most of the mortgage and I paid some payments. My sister has made no payments and never stayed at the home. She co-signed because at the time she made the most money to allow us to qualify for the home. My mother is dead and both my sister and I have inherited the home. She wants half; is this fair. She states she is entitled since she is still held accountable if the home should foreclose because she is on the loan and deed.
Depending on jurisdiction, the fact that you made some payments might give you an ownership share in the house in your own right. What share would be a complex question because you might need to consider both the mortgage payments made and maintenance. Your sister might also be able to argue that she was entitled to some recompense for the risk she describes of co-signing, and that's something that would be very hard to quantify, but clearly you would also be entitled to similar recompense in respect of that, as you also co-signed.
For the share your mother owned, the normal rules of inheritance apply and by default that would be a 50-50 split as JoeTaxpayer said.
You imply that the loan is still outstanding, so all of this only applies to the equity previously built up in the house prior to your mother's death. If you are the only one making the ongoing payments, I would expect any further equity built up to belong solely to you, but again the jurisdiction and the fact that your sister's name is on the deeds could affect this.
If you can't resolve this amicably, you might need to get a court involved and it's possible that the cost of doing so would outweigh the eventual benefit to you.