How important is "realistic" sexism in a Medieval-ish fantasy setting?

Edited to flair sensitive content. My setting is a fantasy mashup of medieval England/Ireland/Wales and early colonial-era America (particularly river towns). The protag is mayor of a provincial but economically important river town. My alpha reader gave this note, which took me aback:

>Your protagonist is a childless unmarried 35 year old woman in a position of political authority in a medieval Europe-inspired setting. I just don't buy that any medieval society would give her that opportunity, especially if children are important.

I respect her opinion, and she made a ton of great points, but "this fantasy society is unrealistically egalitarian/tolerant" is not something I expected to hear from her.

I made a conscious choice to avoid sexism as an obstacle in this world. Is finding a "realistic" level of sexism important?