Arguing

My wife and i went to have a small lump removed from her cheek today. the small wound was dressed and the doctor told her not to remove it for a week. on the way home she tried to remove the dressing and i asked her not to as it was what the doctor told her.
When my wife is asked to do something she will typically do the opposite. yes, she's always been fiesty and i am fully aware of her need to show she can look after herself.
I would like advice on how best to get her to leave the dressing alone.