You Mage Me by Jennifer Wedmore

Eleven months, that’s how long Morwen Rowe had to prepare for the arrival of the Elven Princess. It was finally her turn, and she was terrified. Could she keep the princess safe and alive for thirty days? Or would she be the first mage to fail their mission?
Fauxon Solis had watched Morwen for months, every day she’d stop by his stall and buy herbs, flowers and other items. They made small talk, but never anything more. He never let on he was interested until it was almost too late.
Rowen was wary of Fauxon, was he after the Princess or her? Out of the blue he decides he’s going to help her, they had never interacted beyond a passing exchange. She didn’t know if he could be trusted, but she had to trust her heart because time was running out and she needed all the help she could get.