There shouldnt be any redness or iritation as no products are used on the skin at all.  HOWEVER sometimes there can be a few breakouts of spots after the lymph has been moved around - this shouldnt happen as quickly as the day after but could appear on the honeymoon...!   If it is the first treatment of this kind she has had, I would suggest a week before to give a chance to settle down.   Also, she would get more benefit from a course of treatments however its really nice of you to book it and just the one will leave her feeling very relaxed and uplifted