It's not annoying when a girlfriend wants to look good for her man. It's kinda hot when women take really good care of themselves.
BUT when it comes from a really obvious place of insecurity then it becomes really unattractive really quickly. Because these are the girls that need constant reassurance and outside approval... which tends to mean that they are externally validated, and the next hot guy that comes along can win her attention with his approval.
Women who validate themselves don't get as easily distracted by shiny things like the next more handsome man. Instead these types of women are more secure and stable and attractive longterm.