On which part of allisa mission you're currently at? If you already in the part where he acts like a dog or not (this is the part where i forgot) to cassy. Then you need to go back to the where house and make random encounter ( press seek if you're in mobile. I don't know if in pc) you'll encounter allisa trying to mug you. If i'm no lt wrong, the next mission after that should be you looking a job for her, which can be done by asking in roxie's diner, the rock, and the gentlemen's club. The rock and roxie's diner located in new ark city while gentlemen's club located in the slums (below new ark city).
To ask for the job, go to the manager on the kitchen or employee restroom ( go right immidiately after you enter the place) talk to the bartender for the rock ( talk straight to the person, don't talk to him across the table. He'll only ask what drinks you want) and talk to the manager in gentlemen's club (walk to the upper right after you enter the place). Each of the conversation will have an option for "ask them for alissa to work here" or something. Sorry i kinda forgot some of the conversation.
Note: sorry for the part where allisa act like a dog to cassy happen before or after this encounter.