That’s elder as in elder tree, not older or alder.
She is a Tree Spirit who seems nice enough, provided you respect elder trees. If you don’t, she may take her revenge.
Scandinavian folklore reveals that she particularly dislikes her trees being chopped down to make cradles and cribs. If you put a baby to sleep in an elderwood cradle, HYLDEMOER will come along and pull at the innocent babe’s legs until it shrieks.