It's sexist for YOU other people to want her to wear scanty clothes. It's empowering if SHE wants to wear them.
Of course, the rest of society is not supposed to have any reaction to those clothes that the woman in question doesn't want. If she isn't wearing them for you and you find her sexy, she can be pi$$ed off at you. If you are her colleagues and/or employer and you don't take her seriously, you are taking away her feminist-given empowerment.
The reality is that you ARE allowed to question her judgement within the context you encounter her and you ARE allowed to use that judgement to make decisions that can greatly alter her future (like whether or not to hire her).
And there ain't thing one feminists can do about it.
However, what you can NOT do is use her clothing as justification for committing a crime against her. The crime you commit is still a crime regardless of what she is wearing. What she is wearing, regardless of how it may make you (or others) feel is not justification for a crime.
Personally, I think she is at higher risk if she wears really high heel shoes in a high crime area than if she is otherwise buck naked - simply because it makes it harder for her to run. But even if SHE is committing the crime of public indecency, it does is NO way justify committing crimes against her.
But that doesn't mean you have to hire or promote her.