Theodosia and the Serpents of Chaos by R.L. LaFevers is a cute little GU story set in the early days of the 20th century, that appears to be the first of a series of similar tales.
The eponymous heroine is Theodosia Throckmorton, 11, whose parents work for a museum and specialize in Egyptian antiquities – to the point where they almost entirely neglect her. What they don’t know is that Theo can sense – and remove – all the evil curses that linger on the artifacts. When her mother brings back a particularly powerful item, Theo must battle not only the dark magic, but the powerful men who are trying to use it for their own wicked ends. The fate of Britain, and perhaps the world, is at stake.
She is helped by her younger brother, home from boarding school for vacation, and a cunning pickpocket boy she meets at the train station. Together they steal back the stolen artifact from the adversary and his minions, and Theo stows away to Egypt to return it to its tomb. She is pursued by the adversary, and at the crucial moment manages to thwart him alone.