That whole route takes a long time.
Like, literally. You'll need to busy yourself for a whole lot of in-game days. If you can't get Alissa or Cassie to say something new, try sleeping.
The two parts of her route people most frequently get stuck would be:
- Getting her to interrupt you playing with Cassie in 3 spots. Bed, bath, and by the table when having Cassie change clothes over and over.
- Getting Alissa a job. You yourself need to go to the 3 places that you can work in New Ark and ask the managers about hiring her.