The FNA is likely to be able to answer all the questions as to what the lump is-cancer, non-cancer or normal lymph node. Usually preliminary results come back relatively quickly, 1-3 days or so (even though these days may seem eternally long). If more specialized staining of the tissue is needed or other specialized tests it may take longer to get these results. Generally the answer of cancer or not cancer can be made in the first reviews of the tissue. If, unfortunately, it is cancer the more specialized tests may be needed to help specifically type it and get information about how to treat it.
Having lymph nodes swollen on the other side at the same time actually tends to favor an enlarged lymph node (statistically) although this, too, does not rule out cancer.
Having the previous DCIS does increase the chances of having a recurrent cancer, although it seems a less likely area for breast cancer to spread to. The radiation should have been well focused to minimize exposure of the parotid gland and other structures except those in the direct path of the radiation beam. This makes a secondary tumor in this area less likely but, again, not 100%
I look forward to your update. I completely understand how long the next few days will seem to you. Try not to dwell on it being cancer. Best to stay optimistic and await the answers.
Advice and opinions given are based on the information provided and must not be considered an official medical recommendation. The limitations of the internet prevent an appropriate evaluation. Always consult your doctor if there is concern.