The first two words take on a less common meaning already. "Old medicine" on its own might mean "an expired bottle of Tylenol." The next words, "has a way" treats the medicine like a person, something that has habits and will of its own. This medicine is also capable of haunting the land – that gives it a spirit, like a ghost. Medicine that has will and spirit is powerful and shamanic. This is medicine in the sense of Native American knowledge. This word doesn't belong to me. Dimaline uses it to begin placing us in her world.
Look at the phrases "being remembered" and "was laid." They both imply that someone remembered and someone laid the medicine. But while the medicine directly "has a way... of haunting" the people who remember and lay are pushed out of sight by the passive verb tenses. It feels as if the medicine has more control than the people do.
These are words in the sentence that, rightly or wrongly (and Dimaline will ask us to consider this in the novel) we associate with indigenous people on this continent: old, medicine, remember, land. Each one in the sentence strengthens our association. Words sometimes work by bringing in connotations, drip by drip, until they add up to an impression, like spots of color added to a Monet painting. Artists can create effects from a single splash of an intense color, or from several points of less intense pigments. A writer also can choose several slightly associated words – rather than one strongly associated word – from a field to give readers an association with the field, creating a blatant or subtle effect.
I see another set of words in this sentence: old, haunting, laid. These words draw from the language we use for cemeteries, ghosts, and horror. The sentence would point even more to horror if "laid" was changed to "buried." We use "buried" for the dead and "laid" for the inanimate and the sleeping. Do you taste how "laid" is a little softer and more ambiguous than "buried?" "Laid" also gives the alliteration with "land," which might be worth more to the sentence.
Both "haunting" and "medicine" are strong, specific words. With the rest of the sentence, they build both place and sense of foreboding. This sentence is a hook.