In theory is possible. There is one species of Nicotiana native from Africa (Nicotiana africana). The problem is that this plant is a Namibian endemism, in the other coin of Africa. For people mastering the complicated process of embalm a body, with a trading area that extends to the entire Mediterranean sea, and taking a lot of precise steps and hassles to be sucessful, a local plant able to stop insect damage would had been noticed and treasured. We can speculate that the current Namibian populations are relict populations of a much wider distribution area, and that this is another white rhino. Maybe the north populations were wiped by the old Egyptian empire?, then the flower must appear painted somewhere or some obscure text should talk about such treasure.
And in any case, there is still the Cocaine issue. There are also some members of the family Erytroxylaceae native from Africa, but If you find three of the most popular drugs when putting a sample of a mummy in a machine, you should suspect that either the mummies were fake, or where real but used later to smuggle drugs, or that the drugs were into the machine previously (the laboratory has been used before for analyze drugs).