Charles Rampant
Adventurer
Just FYI:
The player in question tends to treat her characters as walking stat blocks (not just my opinion, players from other campaigns confirm this), and only really seem interested in hurting people. On more than one occasion we've had to restrain her from beating up random NPCs for information (or setting her "torture rat" on them!), which highlights the problems caused by an evil character in a otherwise good-aligned group. The new character is also evil, which is likely to mean more of the same.
My main view on this issue - as a DM, so different than yours as a player - is that there is no golden lasso tying your characters together. I mean, unless you're doing a Fated To Save The World plot or whatever. So if new characters join who turn out to be crazy killers, then your characters should simply eject them. In other words, tell the table that you're not happy with this crazy killer in your group, that your character isn't going to work with them, and that new characters more suitable to the existing makeup of the party should be used. I'm not talking about classes here, but instead about morality; once your party is Good or Evil or whatever, it seems daft to allow drama and unhappiness to exist just because someone wasn't willing to take the memo on that. I'd expect the same if someone joined a party of Rogues and Thieves' Guild types and made a Paladin who then shouted at everyone; why on earth would they accept that person into their ranks and then tolerate their presence?