Looking for a fantasy book (portal, tunnel, glowing creatures, no technology)

Hi everyone,

I’m trying to find a book I read years ago, but I can’t remember the title.

Here’s what I remember:

• It’s about a young woman who was left by her boyfriend.
• She goes into a bookstore and finds a travel guide to a place she doesn’t know.
• She feels strangely drawn to it and decides to travel there.
• To enter this world, she has to go through a long tunnel / passage.
• The portal is only open for a limited time (I think around 2 weeks).
• In that world, no electronic devices work.
• The world itself is more medieval / magical.
• She meets a man from that world (kind of a guide), and there is a romantic storyline between them.
• There is a female villain / ruler (like a witch) who wants to stay in power.
• The most important detail: There are small glowing light creatures (like floating orbs / will-o’-wisps). They attract people, then enter their bodies (under the skin) and kill them.
• I remember a scene where a woman and her children were imprisoned and killed by these creatures.
• There is also a sequel, where these creatures somehow come into the real world.
• The cover (at least in my memory) was purple / lilac with a landscape.

I think it was a young adult fantasy book, probably from around 2000–2015.

Does anyone recognize this book? I’ve been searching for it forever 😅

Thanks a lot!