Rose is a side character who has yet to make on on camera experience. She was Jessie's grandmother. The first mention of Rose occured in the video "Rose." which described her funeral and her death, possibly from an attack by the Rake. This was further fleshed out in The Rose Article where it was revealed that he husband's name was William.
There is also a mention of a "William" and a "Rose" in the original Rake creepypasta further connecting them to both Linnie and The Rake. Whether Jessie's grandparents and the characters mentioned in the creepypasta are the same is unknown.