Blossom Culp and the Sleep of Death by Richard Peck, 1986.

This book starts shortly after the previous book in the series ends.  After Blossom’s old history teacher was run out of town for his scandalous behavior, he was replaced by Miss Fairweather.  Miss Fairweather is a tough, no-nonsense woman who pushes her students to study hard and take history seriously.  Unexpectedly, she comes to appreciate Blossom, an outcast from a poor family, because Blossom demonstrates some knowledge of Ancient Egypt.  Little does Miss Fairweather know that Blossom’s comments in class were inspired by one of the visions that Blossom occasionally gets because of her psychic gifts.

Blossom experiences a visitation from the spirit of an Ancient Egyptian princess who says that she needs Blossom’s help.  Years ago, her mummy and some precious objects were stolen from her tomb.  The princess doesn’t seem to know exactly where her “earthly form” is now, but she’s sure that it’s somewhere nearby.  She’s very concerned because she senses that archaeologists in Egypt are digging to find her tomb and knows that when they finally reach it, they will discover that she isn’t there.  Rather than being concerned about her tomb being violated by the archaeologists, the princess senses that they are searching for her remains in order to venerate them, that if they find her mummy, they will take it to a place of great beauty where it will be treated with the utmost care and respect (a museum).  She wants that and fears that she will miss her chance at the kind of immortality that this form of glorification, care, and study will provide.  So, she asks Blossom to find her earthly remains and inform the searchers of her true whereabouts.  At first, Blossom has no idea how she can accomplish that, but the princess threatens her with a true Egyptian curse if she doesn’t try.

Then, Blossom receives a clue to the mystery in the form of a beautiful Egyptian scarab that her mother found one day while she was out scavenging.  If Blossom can find the place where her mother found the jewel, she can also find the princess’s mummy.  Fortunately, Miss Fairweather has assigned the class special projects about Ancient Egypt, and she is thrilled when Blossom says that she wants to study grave robbers.  Blossom sees this as a good way to collect some extra information about grave robbers that she can use to find the princess’s mummy as well as get a good grade in Miss Fairweather’s class.  It also proves to be an excellent way to draw Alexander Armsworth into her search for the mummy.

Alexander still denies to Blossom that he has real psychic abilities like hers, even after their previous adventures together.  He insists that it was just a phase that they were going through, one that he wants to leave behind.  He’s been busy flirting with Letty, the class snob, and he’s trying hard to get into a prestigious fraternity so that he can give Letty his fraternity pin.  Not only does Blossom think that the boys in the fraternity are a bunch of idiots who do stupid things, but the idea of Alexander giving Letty his pin as a sign of their relationship is just sickening.

Blossom is reluctant to admit her real feelings for Alexander, but the two of them are close in ways that Letty and Alexander never will be because of their shared abilities and adventures, and Blossom has a sense that their futures will be intertwined as well.  Alexander is angry that Blossom is roping her into yet another supernatural escapade, but he has to go along with her project idea because he has already gotten on Miss Fairweather’s bad side and needs to do well on the project to save his grade in class.

Along with the supernatural adventure, there is also a look into the past, the world of 1910s America as well as Ancient Egypt.  First, there are the traditions of stunts associated with Alexander’s initiation into his fraternity and the tradition of giving a girl a fraternity pin as a precursor to engagement (“engaged to be engaged”).  Then, they discover that Miss Fairweather is a suffragette, which is the reason why she left her previous teaching job.  Her feminist ideals cause problems for her in her new, small town when they become known, but with Blossom’s help, she wins over some of the influential women in town as well as a male admirer.

The book is currently available online through Internet Archive.