I'm not sure if there's only one 'accidental wife' novel—sounds like it could be a whole trope shelf at the bookstore. I read one with that exact title by Katherine Garbera. The basic setup is a wealthy businessman and a photographer who have a one-night stand in Vegas and wake up married. Standard fare, but Garbera gives it a twist where the heroine is dealing with some serious family financial pressure, so she tries to make the 'accident' work for a while instead of immediately running for an annulment. The tension comes from them trying to navigate this forced proximity with all their baggage, him being a control freak and her being fiercely independent.
What I actually found more engaging than the central romance was the heroine's relationship with her sister. The subplot about family obligation added some needed grit to what's otherwise a pretty glossy, predictable fantasy. The ending, as you'd expect, involves choosing real love over the convenience of the arrangement. It's a comfort read, not a groundbreaking one, but sometimes that's exactly what you need.