Wrong Side of Forty by Jana DeLeon

It was a day like any other day for Marina Trahan…until she caught her husband in bed with another woman. Before that eye-opening wake-up call, Marina would have described her life as average or uneventful, maybe even boring. But now, chaos and confusion reign supreme. She’d expected to slide through midlife with her unwanted extra pounds, chin hair, and hot flashes and move somewhat gracefully into elastic waist pants and having no verbal filter. But with a wayward husband, a high-maintenance daughter, a lackluster career, and a crazy mother all weighing her down, Marina is ready to wave the white flag of surrender.
Then an intriguing stranger named Alexios shows up out of nowhere and insists she is descended from a goddess and is the only person who can save the world from certain destruction. She has roughly a week to do it. Solving a centuries-old mystery seems like a more interesting proposition than the other situations Marina is facing, so she accepts his challenge. But her search for a magical item of power reveals far more about Marina than she ever knew. Maybe enough to save the world. And even herself.