>>149277697No, but nor is one inclusive of the other. You could famously have an alien oni, for example.
Monster girl requires either a monster that is a girl (e.g. a sphinx) or a monster that has been shaped into a girl (e.g. a shoggoth-girl).
The places you get into exclusivity are robots, animal girls, and furries. A robot can be an alien, but a robot that is simply shaped like a monster doesn't really count as a monster. In really niche cases, if you can have a monster defined by non-physical attributes, you can have a robot that is also a monster, e.g. a succubus turned into a gynoid is still a succubus. Magitech golems also double count as robots and monsters.
Animal girls and furries meanwhile are defined by exclusion. You have to not be an alien, robot, or monster to count. That's why werewolves don't count as either.