I think she is right. I do think that what each generation finds sexy or feminine varies hugely. However you choose to dress now, there are groups of people with whom you will fit right in, you just may have to move to feel that way. There are areas of the UK where the women dress up as if they are going clubbing at any time of day, there are areas where everyone seems to be wearing sports clothes, others where everyone is very casual, there are the farming clothes areas and there are still very hippyish areas. DS seems to like girls in military clothing, judging by the photos I have seen of him at OTC events... You can be what you want to be, wear what you want to wear nowadays, there is a huge choice, but some women will always appear to be more 'feminine' than others without perhaps even realising, even when covered in mud with their hair scraped back and no makeup.
I think if you put all of humanity on a graph, with sexual orientation along one side and masculinity gradually sliding into femininity along the other, you would be surprised at the results.