Good guesses, everyone, but it's actually very simple.
1. She's seeing who can she easily manipulate. Calling out fortune teller as a wolf allows you to see who will vote with you. She can easily kill one of them to support her claims as well.
2. They've already killed off someone who is not voting for them. Having a 6/4 split vote then killing one of the 4, leaving with 3. Killing off one of the 6, who are not wolves, is fine.
3. As long she can control the other 3, the wolves will always have majority. As long as they keep killing off their own members and voting off the stragglers, they can win.
To clarify, 3 wolves (w), 3 followers (f), 3 stragglers (s). Kill 1f tonight = 3w, 2f, 3s to a total of 8. Vote off a straggler = 3w, 2f, 2s = 7 left. Now, they can just kill off a straggler or follower, and it's even 4/5 versus 1/2.
Now, they have to have impeccable social game to keep the followers from straying onto the straggler side. Knowing they have the fortune teller (FT) on their side will prove who to kill off. The FT can easily say, well this straggler is a wolf. Vote them off. They can keep doing this over and over again until they have 3w versus 2 villagers and have majority.