It wasn't the philosophers, it was the coffeehouse owner. Women were pretty much universally banned from European coffeehouses in the 18th century. I'm a little unclear as to whether it was a legal thing or not. She basically just wore men's clothing (fabulous mens' clothing from all accounts) to show that the rule was silly. She was already friends with many of the patrons, and they welcomed her. It sounds more like as long as she wore pants the coffeehouse owner didn't 'officially' know she was a woman. Plausible deniability.