One Good Turn - Meddle & Mend: Regency Fantasy, #2

A reformed thief, a magical viscount, And one good deed that will change a life forever. In the underbelly of London, Nell Birks longs to escape the world of poverty and crime. When she rescues a wealthy gentleman from a gang of thieves, Nell is tasked with robbing the powerful spellcaster Viscount Finlington - as recompense for stealing a mark from a notorious crime lord. Confident that learning magic will improve her chances of a better life, Nell leaps at the opportunity to learn magic from the viscount.
Soon, she finds herself immersed in a glittering social sphere, full of magic, luxury, and exciting possibilities. Dazzled by her new world, Nell quickly learns that with bigger dreams come bigger disappointments. And when her new friends decide to leave London behind, finding her place becomes more urgent than ever. When disaster strikes, everything Nell thought she knew about her old life is shaken to its core.
But if magic is not her key to a better life, she's more lost than when she began.  This new adult fantasy is the second book in the Meddle & Mend series. It takes place shortly after Letters to Half Moon Street but can be read as a standalone.