There was a positive intention (by showrunner Bryan Fuller and writer Michael Green) to have "female voices" be more prominent in the show than in the book.
More of the female voice?
You have to. Because the book is a sausage party. We wanted to have not only Laura represented but to tell Bilquis’ story as well. We have a wonderful episode with Eostre and Kristen Chenoweth playing that role. It wasn’t so much as a gender agenda as much as it was, we need more points of view in this story.
American Gods: Bryan Fuller interview
There was, according to the actor who portrayed Easter, a desire to offer some additional back-story to her character. Gaiman evidently approved.
Did he [Bryan Fuller] tell you what part he wanted you to play? Were you guessing as you were reading?
KC: No, in fact I wasn’t even sure he wanted me—I thought maybe he wanted my opinion. He said, “What do you think about creating the role of Easter?” And, I went, “Oh no. I can’t play Easter, no.” That’s iconic. I mean, she doesn’t speak a lot, but she does very important things. It’s her presence. I said, “She’s just described very differently.” He said, “I want to approach it through these couple angles. I want to unleash and unlock her past.” Then, he kind of explained to me how he saw it with Neil’s blessing too. Then, I went, “Oh. I’m in.”
Jesus comes to Kristin Chenoweth in this week’s American Gods
Gaiman apparently not only approved of the decision to expand the roles but it was, in fact, something that he himself had wanted when writing the original novel but had to sacrifice due to issues of length.
“For us, it was wanting to have a more balanced voice on the show,” said Fuller. “The book has a limited amount of page count in order to tell its story, and if the female characters were fleshed out in a way that Shadow and Wednesday were fleshed out, it would be quite the tone. Neil didn’t have the real estate, and we did as a TV series. Michael and I both love writing for women, and exploring female characters. It just felt like it was absolutely necessary, and there wasn’t ever any choice in the matter.”
In fact, the expansion of Bilquis and Easter were part of the first conversation the duo ever had with Gaiman. Fuller said, “It went to our first conversations with Neil, the idea that this series was going to take a book we love and accordion it out. We asked him, ‘What do you think about expanding those two roles, especially, being in the beginning?’ and his eyes lit up with interest, because those are characters he wanted to do more with himself, but he couldn’t as a first-time novelist [Editor’s note: American Gods wasn’t Gaiman’s first novel] that was already writing a book that was probably frustratingly too long for his editors.”
BRYAN FULLER AND MICHAEL GREEN ON AMERICAN GODS’ WOMEN, S2, AND MOVING BEYOND THE BOOK