Ya, Onion arrested Calindu when there was only 1 mafia member left, meaning Calindu can't be mafia.
Also, Solaris possibly killing a mafia while also being a mafia is within the rules. You would have to know who else is mafia to intentionally harm them. So it's possible she is one because it is very unlikely that, assuming Solaris is mafia, she would know who any other mafia members were that early in the game.
We don't have to kill her yet, Onion can target her tonight and clear her name. Of course, he'll die tonight, buuut who knows.