My grandmother passed away over a year ago, we were never given details of her will and assumed she left nothing. My mother had a stroke 6 years ago, and for the last year had been battling cancer. Upon the death of my mother less then a week ago her sister (whom she has had no contact for several years) is asking for her death certificate. We believe she wants this to take control of whatever was left to my mother or jointly left to them. We believe her sister took and is still taking advantage of the situation. We can see no other reason for her to suddenly ask for her death certificate. What can we do? How can we find this information for little or no money?

Have I got this straight? Your Grandmother passed away a year ago. Your mother, her daughter, died less than a week ago. Your mother's sister, your aunt, is asking for your mother's death certificate.

You believe she wants the death certificate to somehow take advantage of a situation.

The only advantage I can see is if your Grandmother left "something" from your mother in her (your Grandmother's Will). Depending on how the Will was written your mother's "share" of your Grandmother's estate MIGHT pass down to your mother's children (you) OR might be distributed among the children who survive (your aunts and uncles).

Where are you? Have you checked (for free) with the Court in your State that handles probate (will/estate) matters?

In my State - NY - it is very, very difficult to get a copy of the death certificate unless you have a legal reason to do so.

Your mother died less than a week ago and the family is already fighting over her assets - or presumed assets?

... it is very, very difficult to get a copy of the death certificate unless you have a legal reason to do so.
...

The decedent was the mother of OP and the sister of OP's aunt. Either one should be able to get a DC.

Apparently, the aunt is asking OP for the DC. OP might want to first tell the aunt "sure, I'll give you a copy if you first tell me why." Since, of course, aunt could get the DC on her own, a conditional offer such as that might be the best way to learn the information OP wants.

My aunt is a very manipulative person, she took advantage of the fact that mother had a stroke and cut us out of their lives. My grandmother was 90 when my mother had her stroke. We live about 6 hours away. When she started asking for the death certificate we were suspicious. If there is an heirloom the our grandmother thought was something my mother would want we would like to know what it is. There was not a lot of money so we know it's not that.

... If there is an heirloom the our grandmother thought was something my mother would want we would like to know what it is. ...

Your mother? If she is dead, she can't want anything. But if you suspect that a DC might be the key your aunt needs to get possession of such an heirloom, I am unsure how that would be. Perhaps a safety deposit box? Normally, she would have to file a probate petition concerning your grandmother's estate. When she is issued letters of administration, only then would she be able to get into a safety deposit box.