You can use the Genymotion, he is the lightest of all and this hyperlink leads to the download of the free version(Funzone).
You can also opt for the ADV(Android Virtual Device) provided by android studio, but this one consumes many machine resources.
You can choose the IDE Visual Studio Code as an edition. It has "auto complete" for many programming languages and fmw, including some of these you will use to create an RN app, such as: Json, Typescript, Pure Javascript, ES15+, Redux and so on...
If your teacher says you don’t need Android Studio to emulate the system, he meant that does not need in parts. The android studio through their SDK’s will create an image of a SO android with the specifications you chose as well as the hardware settings, and then only be responsible for startar a AVD and can close it quietly... If you set up right your development environment it will be enough to execute
React-Native run-android
and he stará to AVD automatically