Miriam Beckstein discovers an old locket among her birth mother's effects, and realizes that by gazing at it she can transport herself to a parallel world. Physically, the worlds are nearly identical, but her world has developed technologically far beyond the parallel world. Her long lost biological family quickly finds her and explains that she is the heir to a large fortune and, because she has the rare world-walking ability, must be part of the family business. Miriam goes along with it because A)they have guns and B)so do all of her newfound enemies, who want her inheritance. But even as she starts working in the family business, teleporting in between the worlds with trade goods in hand, she's working out ways to modernize the system and maybe even break herself free.
There's a whole subgenre of stories about setting up a typical fantasy scenario (You're the only person left on earth! You've travelled through time! You have stumbled across a vampire conspiracy!) and then having the main character act as sensibly as possible, generally by collecting various gadgets, enlisting helpful friends, and talking everything out. This belongs solidly in that genre. Long stretches are just Miriam buying camping&computer equipment, or Miriam recording her thoughts and theories on the events of the scene before. I found it bland and uninteresting, so I doubt I'll continue with this series.