An unidentified woman was Emily Waltham's mother.
She has never been seen or spoken about in depth, so no one knows anything about her or of her whereabouts. However, this is debatable because in "The One With Ross's Wedding, Part 1", Ross says to Monica that the building he and Emily were getting married in is the one where Emily's parents got married. This leaves a mystery of whom Ross was referring to: Stephen Waltham and his first wife or Stephen Waltham and Andrea Waltham.
She was not present at Emily's wedding to Ross, which makes it appear that she passed away sometime before Emily met Ross.
- The One With Ross's Wedding, Part 1 (Possible mention)