It's her choice, ultimately, but she needs to know she almost certainly will be drawing unwanted attention to herself, and for really no good reason.
I think "unwanted" is a key word here. Dressing in a miniskirt probably will attract more attention, but will it attract more unwanted attention?
If you don't want someone's attention, you send out social signals. It might be clothing, an all-day signal, or it might be short-term, like not looking at them and not smiling. Are there a sizable percentage of people who ignore the latter type of social signal but honor the first type?