For those saying that wearing tank tops to work isn’t professional, maybe you didn’t work at startups before. I worked for uber and very often I wore flip flops and shorts to work. It’s clear that it was sexism of her manager. Otherwise she wouldn’t compare wearing tank tops with wearing see through shirts. By the way, I think both are fine. What’s unprofessional, and sometimes even a crime, is to lower an individual because of the clothes he or she wears.