what rights do i have as a beneficiary

my spouse of thirteen yrs died dec. 4 she changed her beneficiary designation amounts on sept 4th . she had survived cancer for five yrs. she had no will just this policy that left me 50% of the proceeds of the policy. can this be contested.she changed her policy because she could not depend on her daughter, and now her daughter claims that her mother was incompetant at the time. what should i do? there is a signed designation form from her mother and it's on record that it was requested by her mao in august of 2008. ruth died on dec 4th .