Through Shattered Light (Xanadu)

Carissa sees herself as ordinary, average but when she gets dragged through a magic portal, she finds herself in a new body in a new world. Clothing optional. Sex a requirement. The people of this world have little reason to trust intruders particularly when they come with a wizard in tow and Carissa finds herself the king's captive. After one night in his bed, she can't quite remember why that's a bad thing. She knows she has to escape and return to the real world but until she can find a way home, she might as well enjoy the sensual amenities this world provides hot sex with a delicious king and his trusted associate. But the world she's landed in is dying and the people think she's the magical Lady who can save them. She needs to get home before they find out she has no magic and before her heart gets broken. It turns out the wickedly good sex comes with a price she's fallen in love with the king.