Rein, REIN, Lain. This is just a starting point. Please adapt depending on how she acts.
rein (kanji)
Blank look
empty
droopy eyes
stiff posture
feet are parallel or turned inward
The main Rein. According to her voice actor, the keyword for each Rein are gloomy, cool, and like an old man.
REIN (katakana)
cool look
focused eyes
eyes don't droop
looks a bit like Arisu
firm posture
feet point outward
REIN of the Wired. Main points are her strong will and the light in her eyes. Because Rein only calls her the "the other me" and the way she act when switched, we can see he's not that different from the main Rein.
Lain
looks like this
droopy eyes
lack of energy
sometimes wears her clothes like this
The easiest to tell apart. "Goddess lain" is another lain like her. There's also a fresh rein in the last episode.