I've decided that my sim will do the minimum wage grunt work of being a Barista. There are two places in the hood to work at. A bakery / cafe and a fine dining restaurant. At both places she starts working and then staff / owners come and relieve her. No matter how hard I try to cancel the interaction she is pushed constantly to move away from the counter and they take over. There is no interaction that I can see where she can relieve them, the ones who take over. So she is stuck standing behind them waiting for them to move which can be a long time. I was thinking initially that she would put in an 8 hour shift. I don't see how that is possible with the way it is setup.

Is there something I'm missing? Is there a hack / mod to make it less annoying?

It's apparently a bug that was introduced with OFB, and EAxis never fixed it. Try this mod.

Thanks for the suggestion. I am going to try it out. Will report back when I have more info.

Update:

Well it sort of works. They can no longer force relieve my sim which is amazing but when they do try to, after that point, my sim no longer get's +$16 added to her bank account anymore. But it's an easy fix. I just cancel the action and put a new one up. This works until they try again but it doesn't happen as often as it did before so it is better than what I was dealing with before. So thanks.

Since that is a relatively new mod, you might want to post a report/feedback to that mod in the Downloads. The author might not know that it only partially works for some configurations. I know it is a mod I'd like to use, and have downloaded. But I'm a bit squeamish when it comes to trying new mods from creators I don't know. I have enough problems keeping cc sorted, so I haven't added any mods for ages.

I've been using it more and at the bakery it worked like above but at the fine dining restaurant where the owner has assigned a barista it doesn't work. I still have the same problem. I have given up on the idea.

Are you trying to do this on an owned lot? If a playable sim owns the lot and you had them set someone as the barrister that is probably your problem. You can't expect the assigned sim not to try and come back to his job. I would load up the owners and have them unassign the sim and then try again. That mod is supposed to stop visiting sims bugging him by greeting, talking etc.

If the lot is an owned lot then you can actually get the owners to hire her as an employee. Then you can set her job when you're playing the owners.

I could have the owner actually hire her but then she would leave by car to work and time would just be fast forwarded. I want her to go to the lot so I can watch her be a barista. True Joandsarah. Both places are owned by a playable sim, but one place has assigned a barista for the times when I'm not playing this barista working sim.. like another playable sim who goes to the restaurant and wants a cup of coffee. haha. I know, I'm making it difficult. However, there are many coffee drinkers in my hood and only one barista. So most of the time I'm happy to have staff assigned to the coffee machine.

Hmm, in that case why don't you add an extra coffee machine with noone assigned to it. Then when your sim shows up the regular employee should be on one machine leaving the other one free for her.

How do you feel about the increased attractiveness of the barista's Order Coffee caused by the Shopping motive? I find that it's overused along with the Restaurant podium and there shouldn't be as "many coffee drinkers in the hood". But others might disagree, and maybe it accepted as normal that there is a (disorganized) queue for coffee.

All barista's interactions are bugged. It is too easy to get interrupted when purchasing coffee, and the barista can occasionally hang when being pushed to react to rain, among other things.

Okay so thinking what I would do in that situation: When you play family 'A' and take them to the restaurant you would like to see 'sim B' (person playable assigned) run the coffee, but when you load up 'sim c' (Sim you want to follow to work) you want them to be the barista at the same restaurant as sim B, like sims B and C are taking shifts.

I would play the owners rotation first and at the end of the rotation unassign sim B as barista and reassign them to tidy up or something else.
I would then load up and play Sim C's house taking them down to the restaurant to be the barista.

There are other ways that could be done, like Charity suggested add an extra coffee bar so one is always free, but this will mean both will be tending coffee when you play sim C. Using simlogical mods you could even have both sim B and C tend coffee in shifts while playing the owner.

You could also employ sim c and make them a manager, then use Inge's carpool shrub to turn off the carpool, so your sim can skip work without getting fired. Instead of going to work, you can take her to the community lot, reassign the normal barista to some other task, and then have her work as barista.