Yes, I believe that was Mary Hignell, not Hignett, and she was Henry's sister. All the same, I'll try a Hignet search in both England and Wales.
Odd, how my Grandma never talked about her family, and they are still proving quite elusive. I even checked the NYC records to see if he was visiting his Daughter, Mary Jane Diamond, in Brooklyn, or was living with her. Only found one Henry Hignell, who was born in Duchess County, NY in 1865. Nothing in the Immigration records.