How to get plugin name from plugin file location

I think you’ll have to work via get_plugins(). It will return a list of all plugins in your plugin folder, indexed by plugin location – which is the same as your array index. This is also what the plugin administration table uses.

If you only need the data from one file you could also call get_plugin_data() directly. get_plugins() basically just calls that function in a loop, and caches the result.