Fantasy based in Arizona; Girl goes between worlds; "Red haired twins"

[Holly]

Based in Arizona; Girl goes between worlds; political problems in other world, she tries to help. Falls for a king, get pregnant with twins; comes back to our world and has pregnancy and birth. Takes the kids to meet their dad in the other world. "Red haired twins" was important as it signified their father.
I don't remember many details. I read this book years ago when I was in high school or just after (2008-2010 time frame). If anyone can help I really want to find it.

[Kris]

Holly, how does the girl travel between worlds? Spoilers are okay - just give us a clear warning before revealing a spoiler.

How is Arizona referenced in the story?

Is this fantasy novel for older adults or young adults (teens)?

[Holly]

Young adult book. There’s like a tear between the worlds. She finds it accidentally when she’s out hiking I think. It does reference Arizona. The desert specifically. It’s been so long since I’ve read it I don’t remember a lot of details. That’s the problem. :(

[Kris]

Can you tell us more about the heroine - her age, job/skills/interests, family/friends, etc.? How and where she meets the hero?

[Lobstergirl, au gratin]

Holly, are you still looking for this or did you find it?

[Rainbowheart]

If you are, might want to check the Novels Set in Arizona list.