“Yahweh also spoke about Jezebel.” Yahweh spoke via the prophet (cp. 1 Kings 21:19). He did not speak directly Himself. This is a case of the Jewish custom of author-agent.
“The dogs will eat Jezebel by the rampart of Jezreel.” In a culture where family ties were strong and family tombs common, to not have anyone bury your dead body was considered a terrible curse. In fact, many people believed (falsely, but it was a very widely held belief) that a proper burial was important for a comfortable existence in the afterlife. Thus the threat of not being buried but having one’s dead body eaten by animals, birds, and vermin was a horrifying threat of unspeakable loneliness and rejection, both on this earth and in the afterlife (see commentary on Jer. 14:16).
“rampart.” In this case, the “rampart” was the outer wall of the city, often associated with a moat (cp. Darby and JPS, “moat”). Here it more likely just means outer wall. It makes sense that Jezebel would have her personal quarters in the outer wall of the city which would give her a good view of the area around the city, and when she was pushed out the window she would fall to her death at the base of the wall.