I have a theory.
Drones are sterile so sexual pleasure would not be achieved through the act.
Keep in mind the previous three victims, Kane, Brett and Dallas were male.
Xenomorphs seem to sense primarily by pheromone detection.
Due to the differences between male and female hormones, Lambert, being the first female the alien encountered, would have seemed unusual.
The alien, IMO, was using its tail to try and find the source of the pheromones Lambert was giving off. Poor Lambert would have interpreted this differently.
Oh well. At least the damn birds didn't get her.