My grandmother passed away some years back and she hada policy in my mother's name, but to a problem she is having with a sibling she does not have the actual policy or policy number. Is there another way that she can find this policy without having the actual policy number?

Can she call the company and explain the situation?

Are you talking about life insurance?
What do you mean she had it in your mother's name? Was your mother a designated beneficiary of the policy or was the policy covering your mother?

I'm sorry, but please clarify your question with more details so I can help you. Also, I'm not sure who you're referring to each time you use "she"- grandmother, mom, or the sibling?

You will have to know what company it was from.

You go though all of their personal papers, track checking accounts, track all the mail they receive over the next year after death