Forest of Memory, Paperback/Mary Robinette Kowal

Katya deals in Authenticities and Captures, trading on nostalgia for a past long gone. Her clients are rich and they demand items and experiences with only the finest verifiable provenance. Other people's lives have value, after all. But when her A.I. suddenly stops whispering in her ear she finds herself cut off from the grid and loses communication with the rest of the world. The man who stepped out of the trees while hunting deer cut her off from the cloud, took her A.I. and made her his unwilling guest. There are no Authenticities or Captures to prove Katya's story of what happened in the forest. You'll just have to believe her.