From a behavioral point of view a well presented person not only feels better but their environment treats them better to, people simply respond better and have higher expeditions of a well presented person. This especially includes their personal bodily care like their hair, etc. but includes dress too. She may be expressing her feelings because she may think that you are letting yourself down in a way that would effect the way people in your life treat you.
It's a tough one really although I can see the logic, I don't think id be too happy about it either, it comes over bit offensive whatever way you look at it.