Call ? I think you could start researching about her story. There is many books, 'usually' people don't simple cast a spell for any entity appear. In "her" case, you should build a relationship, but this include know about each other right? To start, do you know her name?
Re: The triple goddess!
By: Lark Moderator / Knowledgeable Sep 05, 2014
Post # 3
The Triple Goddess is a completely modern concept which is based on the book "The White Goddess" by Robert Graves. In this she is seen as representing Maiden/Mother/Crone. You won't find this is ancient mythologies although some people try to shove these Goddesses into that modern concept. It doesn't really work though. You'd do better to find a single Goddess that you feel drawn to and develop a relationship with her.
Lark is correct, she is a concept, not a deity. But you can pray to the mother goddess, Gaia. She is the Greek mother of all, the new-age mother Earth, some Mormons believe she is based off Heavenly Mother (God the Father's wife). (She's also the tree of life in the Book of Mormon). So, I'd go with her if I were you.