Richard Shackleton was living in Knowlton, Sussex, NJ 1780-1793 and I assume they married there. I'd take a look at the Sussex County Historical Society's web site, www.sussexhistory.org/annals/
who has births, marriages and deaths plus a lot of other records.
I see she was buried in Warren County and assume she died there too. I'd contact the Warren County Library, http://warrenlib.org/node/1561#.WGhS939uNVc
who has newspapers and ask about a scan/copy of her newspaper death notice. Her parents might be mentioned in it. Successful Searching!