Outlander certainly seems to include a lot ... It is possible that Gillian Edgars chose the name Geillis when she went into the past because of her knowledge of Scottish history.

In the promo for Outlander season 7 ... This was when she went by her legal name in 1968, Gillian Edgars. When she was in the past, she killed two more husbands. The first was Arthur Duncan.