Obviously from reason as of right now, Farrah should consider staying home just to make sure she doesn’t spread germs.
Option A, wearing a mask would help if she was conditional (semi-healthy) but because you mentioned that Farrah is in a rough shape, the mask really won’t do too good as it cannot completely filter the air.
Option C, avoiding contact is a finer solution but for how long can you stay away from interactions? You would have to interact with the materials such as desks, chairs, pens, etc. Others are most likely to use those same material which would cause unwanted spreading through indirect contact.
Option D, coming back home after lunch is also a reasonable answer but their is no mask/avoidance of contact induced, your just working normally as you would on a regular day. This can cause several health issues to rise as you aren’t taking the precautions you should. And even if you are, there is no guarantee you would be able to do your job as you are in a position where your health is at risk.
Even if your options are limited, or your situation isn’t ideal, you should never put your own health and other’s health at risk.
Staying at home is doing the favour for both you and those around you.
Hope this helped!!