Interspousal transfer Deed

Recently my sister's husband passed away. They have been married for 20 years they purchased their house during the marriaged and they live in California but my sister just found out that he did not put her name on the Deed and he made her signed a interspousal transfer deed which she was not aware or understood what she was signing. She just found out everything because she is going through a probate and her husband kids are contesting the house. Her husband died without will. Throughout the marriaged my sister contributed all thier finances she held to jobs just to maintain their household expenses. Does my sister have any legal right to the house since she sign the insterspousal transfer deed which she was not aware of because her husband tricked or did not explained what she was signing? Thank you any help will be greatley appreciated.