Swollen oral glands after double mastectomy

My wife had a double mastectomy a few months ago.  The surger included the removal of 14 lymph nodes.  She received 28 radiation treatments but no chemotherapy.  She now suffers from swelling of the tongue, lips, cheek, front of throat (thankfully, not all at the same time).  This began shortly after starting arimidex.  But removal of arimidex (and for that matter all other medication, both prescription and OTC) has not solved the problem.  The swelling occurs with no aparent trigger and no discernable timing.  It may occur every other day, or weeks apart.   It usually develops while she is sleeping (rarely severe enough to wake her), and goes away over 4 to 12 hours without any medication.  Antihistamines (e.g. benadryl) have no apparent preventive or curing effects.  She has been tested for allergies and has seen an ENT specialist.  All to no avail.  Needless to say, going to sleep is most certainly stressful if not down right terrifying.  Has any one else seen this?  And if so, what can be done?