Mask by Andrea Fink

    I found this one on kindle unlimited for free.  Emily was busy leading a quiet life when a strange man shows up at her home with a young woman who appears unconscious.  He pushes his way into her apartment, tells her the young woman is her sister and that she's been cursed and only Emily can help. 

Further, both this man and Emily's sister live in another world where magic is very real and both Emily and her twin are part human, part demon and therefor have magic.  Apparently, her sisters gifts are somewhat limited by Emily's are not.  She was exiled as a baby to the human world with her mother because she was the second born and her father didn't want her to be a danger to her sister.

So Emily is thrust into unfamiliar circumstances forced to pretend to be someone she's not.  She faces a lot of challenges along the way, not the least of which is her attraction for a vampire named Wit, who is NOT her sister's fiance.

This is part of a series.  It was engaging, not sure how I feel about continuing.  I gave it 3 out of 5 stars.