PBA: It depends on why you’re doing it. If it’s out of comfort or style, then no, it’s not assur. If you’re doing it to try and be more “frum”, then yes, I’d say it is.
1. Why do you assume she was doing it to be more frum? Maybe she is just embarrassed to stand with 25k men staring at her (I would be)?
2. That is simply not the halacha; you are simply wrong. It is not baal tosif to be machmir on tznius. Perhaps if you claim it is min hadin, but nobody has made such a claim .
Anti-semite.