That should be attainable with the current product. If the days are required and there is a minimum paid time requirement, then all agents assigned to the work plan will be scheduled.
The scheduling engine is free to choose amongst any set of daily shift configurations each day as long as it results in a valid weekly shift.
I am not sure if you might be suggesting that you want one amongst several daily shifts to always be chosen for Joan - if that is the case, then she will need her own work plan with just the one shift configuration per day.
Agents are assigned to work plans not daily shift configurations. So, if you have, for example, a 'Morning Flex' work plan that has several daily shifts for each day (e.g., 2h no breaks or meals; 4h one break; 6h one break and one meal; 8h with two breaks and one meal - all/some with variable start windows, etc.), but you want a subset of agents to have very specific shifts, then you want those agents to be assigned to a more specific/targeted work plan (e.g., "9am-2pm", "Morning 40h", etc.).
I would suggest opening a support ticket for further assistance.