Shadow Wife by Diane Chamberlain

Joelle D'Angelo's best friend, Mara, is left with brain damage after she suffers an aneurysm whilst giving birth to her son. Alone and grieving, Joelle turns to the only other person who understands her pain, her colleague, and Mara's husband, Liam. What starts out as comfort between friends gradually becomes something more.

Torn by guilt and her impossible feelings for Liam, Joelle sets out to find help for Mara, no matter how unconventional the source. Her search leads her to California, and into the life of a woman shrouded in mystery. Carlynn Kling Shire is a healer and, according to Joelle's parents, saved Joelle's life when she was an infant. As Joelle is guided down an unfamiliar path by a woman with her own shocking secrets, she discovers that while some love is doomed, some love is destined to survive anything.