Helen Swan was the wife of Geoffrey Swan, the mother of Charlie Swan, the grandmother of Bella, grandmother-in-law of Edward Cullen, and great-grandmother of Renesmee Cullen. She never appeared in the series, but she was mentioned at Bella's wedding.
It is mentioned in The Twilight Saga: The Official Illustrated Guide that she and her husband Geoffrey did not think they could have children, so Charlie was an unexpected, but welcome, surprise. He was born when Helen and Geoffrey were in their mid-40s.
By the time their son reached adulthood, Helen developed early stages of Alzheimer's disease, and Geoffrey's mobility was curtailed by severe arthritis, which kept Charlie from going to college.
After Charlie married Renée and had Bella, their conditions worsened. When Renée left with Bella, Charlie remained in Forks to take care of his parents, though he really wanted to follow them. In 1991, within 6 months of each other, Geoffrey and Helen passed away, leaving Charlie alone.
- "They were your Grandma Swan's… We had a jeweler replace the paste stones with sapphires."
- ―Charlie, on the wedding present he and Renée give Bella.[src]
At the beginning of Breaking Dawn, Bella inherited two hair combs in silver, which used to belong to Helen, as wedding presents from her parents and her "something old and something blue", though the combs' pastestones were replaced with sapphires. In the movie, there was only one comb.
Life and Death: Twilight Reimagined