I would just reply "Sue can eat whatever she wants because she doesn't care about her health, but I do, sorry but I will have to pass" lol
Likely this will cause sue to confront you, at which point you can ask her about her HbA1c and inform her that she is very much outside of the medically accepted range for "good control" and being outside of this range simply shows Sue that she does, by all definitions have 'poor control' of her diabetes and if she did care about her health she would take her disease seriously and work to fix this.
Remind her that ever day she may be free of complications until one day she won't be. You plan on preventing that day for a long time. .