It's also worth highlighting that, even if a character is Taken Out in a social conflict, they have some say in how they respond.
So a PC might intimidate a cop into backing off, but you can decide that the cop backs off because he doesn't want any innocent bystanders to get hurt, rather than being afraid of the PC in question.
If this cop Conceded, rather than got Taken Out, you do know you get to decide how she loses the conflict, right? Though I'm not sure a full Social Conflict is appropriate just to try and get some tear gas. That's more likely a single Challenge roll.
Is she bound to help them in the fight? If they're intimidating her (which I'm assuming since you said their only social skill is Intimidation)* I can't imagine she's helping them because she likes and trusts them. Can you tell us more about her situation?
In terms of having a single (or a small number) NPC with the group, it's really up to you how to handle it. If you want, you can roll dice for her like a player would for their character, or you can just rule that she does what you need her to without dice rolls.
One of the nice things about the conflict mechanics is that characters in a conflict are divided into teams. If you have three PCs and three vampires, each pairing of one PC and one vampire is a single team, and for the duration of the conflict, you can only take on the opposing character in your team. Once those teams have fought it out, you can have the "survivors" start a new conflict if you wish, but it makes it very easy to keep allied NPCs from adding too many dice rolls or taking the spotlight away from the players by putting them in a team of their own, separate from the PCs.
*As an aside, they must have pretty rubbish Social Stress and defence if they don't have Empathy and Presence, correct? Getting into a lot of Social Conflicts could go very badly for them...